internalising symptoms and executive function difficulties ...epubs.surrey.ac.uk/849640/1/e-thesis...
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1
Internalising symptoms and executive
function difficulties in adolescents with
and without Developmental Coordination
Disorder
Serif Omer
Submitted for the Degree of
Doctor of Psychology (Clinical Psychology)
School of Psychology Faculty of Health and Medical Sciences
University of Surrey
Guildford, Surrey
United Kingdom
September 2018
2
Abstract
Background: There is growing evidence that individuals with Developmental
Coordination Disorder (DCD) experience elevated internalising symptoms and
executive function (EF) difficulties compared to their typically developing (TD)
peers. Research also suggests that EFs are important for psychological wellbeing.
Aims: This study aimed to explore whether adolescents with DCD experience
greater levels of internalising symptoms and everyday EF difficulties than their TD
peers. It also explored whether EF difficulties mediate the relationship between DCD
status and internalising symptoms. Methods and procedures: Fourteen adolescents
with a diagnosis of DCD and 29 TD adolescents (ages 12-15) participated. A cross-
sectional survey was conducted to collect parent-reported EF difficulties and self-
reported internalising symptoms. Outcomes and results: Self-reported internalising
symptoms and parent-reported EF difficulties were significantly higher in the DCD
group compared to the TD group. A bias-corrected, bootstrapped mediation analysis
identified that the effect of DCD on internalising symptoms was mediated by parent-
reported EF difficulties. Exploratory analyses identified that this indirect effect was
greatest for symptoms of depression through behavioural regulation difficulties.
Conclusions and implications: These findings support previous research indicating
that adolescents with DCD experience greater levels of internalising symptoms and
EF difficulties than their TD peers. This highlights the need for increased awareness,
routine screening, and intervention for mental health and EF difficulties in people
with DCD. The findings also highlight the potential benefits of targeting EF deficits
in people with DCD to improve emotional wellbeing. However, larger scale,
longitudinal research is needed.
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Keywords: Developmental Coordination Disorder, DCD, internalising
symptoms, depression, anxiety, executive functions
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Acknowledgements
I would like to express thanks to my research supervisor, Dr Hayley Leonard,
for her support and expertise throughout all aspects of this research project. I would
also like to acknowledge Ana M. Jijon for her assistance with the data
collection/extraction for the literature review and Dr Harriet Tenenbaum who
provided critical feedback on the meta-analysis.
I am very grateful to the Dyspraxia Foundation for their help distributing
recruitment advertisements for the empirical research study. I would also like to
thank the schools and youth clubs that supported with data collection. I would like to
thank all the young people and their parents who kindly volunteered their time to
participate in my research.
Finally, I would like to thank my university tutors and placement supervisors
who have supported me throughout the clinical training programme.
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Publications and presentations
Parts of this thesis have been published in:
Omer, S. (2018, June). Executive function and internalising problems in adolescents
with Developmental Coordination Disorder. Paper presented at the UK’s 7th
biennial academic and practitioner conference on Developmental
Coordination Disorder, Brunel University London, London.
Omer, S., Jijon, A.M., & Leonard, H.C. (In press). Internalising symptoms in
Developmental Coordination Disorder: A systematic review and meta-
analysis. Journal of Child Psychology and Psychiatry.
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Table of Contents
Page
Abstract 2
Acknowledgements 4
Publications and presentations 5
Part 1: Major Research Project Empirical Paper - Internalising symptoms
and executive function difficulties in adolescents with and without
Developmental Coordination Disorder
7
Abstract 8
Introduction 10
Method 19
Results 27
Discussion 37
References 50
List of appendices 70
Appendices 71
Part 2: Major Research Project Literature review - Internalising symptoms
in Developmental Coordination Disorder: A systematic review and meta
analysis
122
Abstract 123
Introduction 125
Method 129
Results 135
Discussion 154
References 160
Appendix 173
Part 3: Summary of Clinical Experience 174
Part 4: Table of Assessments Completed During Training 177
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Part 1: Major Research Project Empirical Paper
Internalising symptoms and executive function difficulties in adolescents
with and without Developmental Coordination Disorder
Word count: 9420
Statement of Journal Choice
Research in Developmental Disabilities
“Research in Developmental Disabilities” primarily publishes empirical studies of an
interdisciplinary nature that contribute to the understanding of problems associated with
developmental disabilities. It has published numerous cross-sectional studies
investigating the impact of Developmental Coordination Disorder. See Appendix A for
more details.
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Abstract
Background: There is growing evidence that individuals with Developmental
Coordination Disorder (DCD) experience elevated internalising symptoms and executive
function (EF) difficulties compared to their typically developing (TD) peers. Research
also suggests that EFs are important for psychological wellbeing. Aims: This study
aimed to explore whether adolescents with DCD experience greater levels of
internalising symptoms and everyday EF difficulties than their TD peers. It also
explored whether EF difficulties mediate the relationship between DCD status and
internalising symptoms. Methods and procedures: Fourteen adolescents with a
diagnosis of DCD and 29 TD adolescents (ages 12-15) participated. A cross-sectional
survey was conducted to collect parent-reported EF difficulties and self-reported
internalising symptoms. Outcomes and results: Self-reported internalising symptoms
and parent-reported EF difficulties were significantly higher in the DCD group
compared to the TD group. A bias-corrected, bootstrapped mediation analysis identified
that the effect of DCD on internalising symptoms was mediated by parent-reported EF
difficulties. Exploratory analyses identified that this indirect effect was greatest for
symptoms of depression through behavioural regulation difficulties. Conclusions and
implications: These findings support previous research indicating that adolescents with
DCD experience greater levels of internalising symptoms and EF difficulties than their
TD peers. This highlights the need for increased awareness, routine screening, and
intervention for mental health and EF difficulties in people with DCD. The findings also
highlight the potential benefits of targeting EF deficits in people with DCD to improve
emotional wellbeing. However, larger scale, longitudinal research is needed.
9
Keywords: Developmental Coordination Disorder, DCD, internalising
symptoms, depression, anxiety, executive functions
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Introduction
Developmental Coordination Disorder (DCD) is a neurodevelopmental disorder
affecting between 5-6% of children (American Psychiatric Association, 2013). It is
characterised by significant impairment in motor coordination which interferes with
everyday life, is evident in the early developmental period, and cannot be explained by
another medical condition or intellectual disability. Individuals with DCD might have
difficulties with self-care (e.g. tying shoe laces, brushing teeth), leisure activities (e.g.
catching a ball, balancing) and academic tasks (e.g. handwriting). However, the impact
of DCD also extends beyond these difficulties with motor tasks. Research has identified
that DCD can impact on a wide range of physical, social, and psychological domains
(Zwicker, Harris, & Klassen, 2013) and that difficulties can continue through childhood
into adulthood (Cousins & Smyth, 2003; Hill, Brown, & Sorgardt, 2011). Given the
relatively high prevalence of DCD, and evidence that it is often poorly understood by
healthcare and education professionals (Gaines, Missiuna, Egan, & McLean, 2008; B. N.
Wilson, Neil, Kamps, & Babcock, 2013), research exploring the wider impact of the
condition is important to develop more effective, holistic interventions for this
population.
DCD and internalising symptoms
One area that has recently received increased attention is the impact of DCD on
an individual’s mental health, specifically internalising symptoms (Mancini, Rigoli,
Cairney, Roberts, & Piek, 2016). ‘Internalising’ is a broader construct referring to
symptoms of both depression and anxiety, which have been found to commonly overlap
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in childhood and adolescence (Eaton et al., 2013; Kovacs & Devlin, 1998). A systematic
review and meta-analysis of the literature identified that children and adolescents with
DCD experience greater levels of internalising symptoms than their TD peers (see Part
2). Although the reviewed studies tended to adopt a cross-sectional design, two
longitudinal studies were identified that found that a diagnosis of DCD in childhood
predicted internalising symptoms later on in adolescence (Harrowell, Hollén, Lingam, &
Emond, 2017; Wagner, Jekauc, Worth, & Woll, 2016). Research investigating this
relationship in community samples of children (i.e. not specifically focusing on
individuals diagnosed with DCD) has also identified that poor motor skills in childhood,
measured as a continuous construct, predict internalising symptoms in adolescence
(Piek, Barrett, Smith, Rigoli, & Gasson, 2010; Sigurdsson et al., 2002) and adulthood
(Poole et al., 2015). Additionally, there is evidence that interventions focused on
improving motor skills can have a positive effect on mental health (Piek et al., 2015).
Together, these findings would suggest a causal relationship between DCD and mental
health difficulties.
The Environmental-Stress Hypothesis was introduced as a framework to
understand this relationship (Cairney, Rigoli, & Piek, 2013). It proposes that the motor
impairments in DCD can expose an individual to a range of secondary psychosocial
stressors which, over time, can result in greater levels of internalising symptoms. Recent
research has explored a number of these secondary stressors, providing support for the
Environmental-Stress Hypothesis. For example, there is evidence that increased peer
victimisation (Campbell, Missiuna, & Vaillancourt, 2012), reduced leisure activities
(Raz-Silbiger et al., 2015), poorer self-esteem (Rigoli, Piek, & Kane, 2012), physical
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inactivity (Li et al., 2018), reduced social support (Rigoli et al., 2017), and lower
perceived academic performance (Lingam et al., 2012) may all mediate the relationship
between motor difficulties and internalising symptoms. The findings would suggest that
targeting these psychosocial factors, in addition to the motor difficulties, could have
beneficial outcomes for the emotional wellbeing of people with DCD. As such, further
research exploring the mediating factors through which DCD might impact on
internalising symptoms will have important implications for treatment in this population.
DCD and executive function
Recent research has also investigated the role of executive functions (EF) in
DCD. EFs refer to a set of higher-order cognitive processes that regulate, monitor and
control cognition, emotions and behaviour in order to achieve a particular goal
(Diamond, 2013). Three core EFs have been identified consisting of inhibition (i.e. the
ability to control natural responses or ignore irrelevant stimuli), working memory (i.e.
the ability to temporarily hold information in mind whilst simultaneously manipulating
information) and cognitive flexibility (i.e. the ability to switch between thinking about
different concepts or tasks), which together underlie more complex EFs including
planning, problem solving and reasoning (Miyake et al., 2000).
It has been highlighted that there is an important overlap in the development of
motor skills and EFs, with both sharing underlying neural pathways involving the
prefrontal cortex and cerebellum (Diamond, 2000; Koziol, Budding, & Chidekel, 2012).
Compromise to these neural pathways has been implicated in the motor difficulties
experienced by people with DCD (Biotteau et al., 2016). As such, research has also
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found that individuals with DCD perform worse on a wide range of EF tasks compared
to their TD peers (Leonard & Hill, 2015; P. H. Wilson, Ruddock, Smits-Engelsman,
Polatajko, & Blank, 2013). This includes performance-based tasks of inhibition
(Mandich, Buckolz, & Polatajko, 2002), working memory (Alloway, 2007), cognitive
flexibility (Wuang, Su, & Su, 2011) and planning (Piek et al., 2004). Individuals with
DCD also self-report greater difficulties with EF in their everyday life compared to TD
controls (Tal Saban, Ornoy, & Parush, 2014). Additionally, findings from longitudinal
studies have found motor difficulties in childhood predict EF difficulties at a later age
(Bernardi, Leonard, Hill, Botting, & Henry, 2018; Michel, Roethlisberger,
Neuenschwander, & Roebers, 2011). This would suggest that EF impairments are a
significant feature of DCD and may be inextricably linked to the motor difficulties that
characterise the disorder.
Executive function and internalising symptoms
Despite growing evidence that individuals with DCD experience greater levels of
both internalising symptoms and EF difficulties compared to their TD peers, there has
been no attempt to explore the relationship between the two within this population. The
Environmental-Stress Hypothesis has been an important contribution to the field in
understanding how motor difficulties can contribute to elevated internalising symptoms,
however it only considers the role of physical and psychosocial factors. Given the
impact of DCD on EFs, it is important to consider how these higher-order cognitive
processes might also impact on the mental health of individuals with DCD.
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There is a growing body of literature highlighting the importance of EFs for
mental health. Meta-analytic reviews have identified EF deficits in both children
(Wagner, Müller, Helmreich, Huss, & Tadić, 2015) and adults (Snyder, 2013; Snyder,
Kaiser, Warren, & Heller, 2014) with depression and anxiety disorders. Neuroimaging
studies have also found the brain networks involved in EF to be atypical in individuals
with mood disorders (Koenigs & Grafman, 2009; Price & Drevets, 2010). Additionally,
there is evidence to suggest that EF difficulties precede internalising symptoms in
children and adolescents. For example, working memory (Evans, Kouros, Samanez-
Larkin, & Garber, 2016; Letkiewicz et al., 2014), inhibitory control (Lengua, 2006;
Martel et al., 2007; Nigg, Quamma, Greenberg, & Kusche, 1999; Riggs, Blair, &
Greenberg, 2003), cognitive flexibility (Evans et al., 2016) and global EF difficulties
(Han et al., 2016) measured during childhood have been found to prospectively predict
internalising symptoms. In support of this relationship, improvements in EF have been
found to mediate the positive effects of neurocognitive intervention programmes on
reducing internalising symptoms in children (Riggs, Greenberg, Kusché, & Pentz, 2006).
Together, these findings highlight the role of EF in mental health and the potential
importance it has for people with DCD.
The relationship between EFs and internalising symptoms can be understood
through a variety of possible pathways. One explanation is the role of EFs in emotion
regulation. Emotion regulation refers to the process of actively changing the intensity or
duration of an emotional response (Koole, 2009). High levels of maladaptive emotion
regulation strategies (e.g. avoidance, rumination, worry) and low levels of adaptive
emotion regulation strategies (e.g. problem solving, cognitive reappraisal) have been
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associated with internalising symptoms (Garber, Braafladt, & Weiss, 1995; Mezulis,
Priess, & Hyde, 2011; Silk, Steinberg, & Morris, 2003). It has been suggested that EFs
play a key role in the effective use of these strategies (Joormann & D’Avanzato, 2010;
Schmeichel & Tang, 2015; Wante, Mezulis, Beveren, & Braet, 2017). For example,
cognitive flexibility impairments have been linked to increased internalising symptoms
through perseveration of negative thinking, such as worry and rumination (Brosschot,
Gerin, & Thayer, 2006; Demeyer, De Lissnyder, Koster, & De Raedt, 2012; Johnson,
2009). Difficulties with inhibition have been associated with depression through
increased rumination and reduced reappraisal strategies (Joormann & Gotlib, 2010).
Difficulties in updating working memory have also been linked with depression and
anxiety through increased rumination and worry (Meiran, Diamond, Toder, & Nemets,
2011; Owens, Stevenson, Hadwin, & Norgate, 2012). Generally, this research indicates
that individuals with EF deficits find it harder to shift their attention away from negative
emotional information and use fewer adaptive strategies, which contributes to higher
levels of depression and anxiety. In addition to emotion regulation, EFs are also
important for academic functioning (Best, Miller, & Naglieri, 2011) and social skills
(Dawson, Shear, & Strakowski, 2012). Difficulties with each of these areas can also
have implications for emotional wellbeing (Ende, Verhulst, & Tiemeier, 2016; Nilsen,
Karevold, Røysamb, Gustavson, & Mathiesen, 2013; Zhang, Zhang, Chen, Ji, & Deater-
Deckard, 2018).
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The present study
Given the emerging evidence that individuals with DCD experience deficits in
EF abilities and the role that these higher-order cognitive processes have in
psychological wellbeing, it is likely that these deficits have important implications for
the mental health of people with DCD. To date, no research has investigated this
potential relationship between EF difficulties and internalising symptoms in DCD.
However, parallels can be drawn from research with other neurodevelopmental disorders
that impact on EF. For example, Gardiner and Iarocci (2018) found an association
between parent-rated EF difficulties and depression in children with an autism spectrum
disorder (ASD), suggesting that improving EFs could be an important target for reducing
internalising symptoms. More specifically, Lawson et al. (2015) found that a diagnosis
of ASD, compared to a TD group, predicted difficulties with cognitive flexibility which
in turn predicted higher levels of anxiety and depression. This suggests that individuals
with ASD experience greater levels of internalising symptoms than their TD peers and
that this relationship may be mediated through EF difficulties. EFs have been found to
have a similar explanatory role for the high levels of internalising symptoms
experienced in other childhood disorders, including spina bifida (Kelly et al., 2012).
The purpose of the present study, therefore, was to investigate EF difficulties and
internalising symptoms in adolescents with and without DCD to better understand these
difficulties in the disorder. First, the study set out to replicate previous research findings
that adolescents with DCD have higher levels of both EF difficulties and internalising
symptoms compared to TD adolescents. Second, it explored whether the impact of DCD
on internalising symptoms is mediated through the difficulties in EF that are often
17
reported in this population (see Figure 1). Adolescents were chosen as the focus for this
study given that much of the research into internalising symptoms in DCD has focused
on pre-adolescent children (see Part 2). Furthermore, there is some suggestion that the
impact of DCD on mental health may be greater for adolescents compared to younger
children (Missiuna, Moll, King, King, & Law, 2007; Skinner & Piek, 2001). Given that
adolescence is also generally considered a time of high risk for mental health difficulties
and an important period for the ongoing development of EFs (Blakemore & Choudhury,
2006; Ernst, Pine, & Hardin, 2006; Twenge & Nolen-Hoeksema, 2002), focusing the
present study on this age group was deemed highly relevant.
Figure 1. Mediation model depicting the indirect effect of DCD status on internalising
symptoms through EF difficulties
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Previous research into EFs in DCD has focused predominantly on performance-
based measures of EF (Leonard & Hill, 2015; P. H. Wilson et al., 2013). Although these
tasks are useful for assessing the specific impact of DCD on individual components of
EF in controlled conditions, there is an argument that they do not always represent
functioning in the ‘real-world’ environment (Burgess et al., 2006; Toplak, West, &
Stanovich, 2013). Therefore, studies adopting more ecological measures of EF
difficulties, such as behaviour rating scales, are also necessary to complement the
findings from standardised, laboratory-based tasks. Indeed, Tal Saban et al. (2014) found
greater EF deficits in adults with DCD compared to TD adults based on self-report of
everyday EF difficulties. However, no prior research has explored everyday EF
difficulties in adolescents with DCD using such measures. Therefore, the present study
adopted a behaviour rating scale as its measure of EF (Gioia, Isquith, Guy, &
Kenworthy, 2000) to better understand how EF difficulties in day-to-day life are
impacted by DCD in adolescents.
A self-report measure of internalising symptoms (Ebesutani et al., 2012) was
adopted for the present study, given that parents may under-report the emotional
difficulties of adolescents (Cantwell, Lewinsohn, Rohde, & Seeley, 1997; Hope et al.,
1999; Smith, 2007; Sourander, Helstelä, & Helenius, 1999). A parent-reported measure
of everyday EF difficulties was used to minimise the impact of common method bias
that could otherwise be problematic for mediation analyses if self-report measures are
used for both the mediator and dependent variable (Podsakoff, MacKenzie, Lee, &
Podsakoff, 2003; Podsakoff, MacKenzie, & Podsakoff, 2012).
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The present study, therefore, had three main hypotheses: (1) adolescents with
DCD would have greater self-reported internalising symptoms than TD adolescents; (2)
adolescents with DCD would have greater parent-reported EF difficulties than TD
adolescents; and (3) parent-reported EF difficulties would mediate the relationship
between DCD status (i.e. DCD vs. TD) and self-reported internalising symptoms (see
Figure 1).
Method
Design
The study adopted a quantitative cross-sectional design to measure EF
difficulties and internalising symptoms in a group of adolescents with DCD and a group
of TD adolescents at one point in time.
Participants
DCD group. Participants were eligible for the DCD group if they met the
following criteria: (i) a diagnosis of DCD which was confirmed by the researchers
through inspection of clinical reports, (ii) aged 12-years-0-months to 15-years-11-
months, (iii) scored ≤57 on the Developmental Coordination Disorder Questionnaire –
07 (DCDQ-07) to confirm the current presence of motor difficulties (see measures), and
(iv) had a parent/guardian willing to complete questionnaire measures. Adolescents were
excluded if they had a comorbid diagnosis of Attention Deficit Hyperactivity Disorder
(ADHD) or ASD, as reported by their parents, so that findings could be more easily
attributed to DCD. They were also excluded if they lived outside the United Kingdom
20
(UK), due to international variations in diagnosis and intervention, or if any of the
questionnaire measures were missing. Participants with DCD were recruited through
advertisements distributed via a national charity, registers of participants from previous
studies, a secondary school in England specialising in specific learning difficulties, and
word of mouth. Thirty-nine adolescents and their parents responded to the
advertisements, of which 30 went on to complete the initial screening questionnaire.
Fifteen were subsequently excluded due to the adolescent being older than 16 (n = 4),
reporting a diagnosis of ADHD (n = 2), reporting a diagnosis of ASD (n = 7), living
outside the UK (n = 1), or not providing clinical reports to confirm their diagnosis (n =
1). Of the remaining 15 participants that went on to complete the questionnaire
measures, the Revised Child Anxiety and Depression Scale – Short Version (RCADS-
25) was missing for one participant. As such, the DCD sample consisted of 14
adolescents and their parents.
TD group. Participants were eligible for the TD group if they met the following
criteria: (i) aged 12-years-0-months to 15-years-11-months, (ii) scored ≥58 on the
DCDQ-07, and (iii) had a parent/guardian willing to complete questionnaire measures.
Adolescents were excluded if they had a diagnosis of DCD, ADHD or ASD, as reported
by their parents. They were also excluded if they lived outside the UK or if any of the
questionnaire measures were missing. TD participants were recruited through
advertisements distributed via secondary schools and youth clubs in south-east England,
registers of participants from previous studies, and word of mouth. Forty adolescents
and their parents responded to the advertisements, of which 37 went on to complete the
initial screening questionnaire. Four were subsequently excluded due to the adolescent
21
being older than 16 (n = 2), reporting a diagnosis of ADHD (n = 1), and reporting a
diagnosis of ASD (n = 1). Of the remaining 33 participants that went on to complete the
questionnaire measures, three had scores below the cut-off on the DCDQ-07 and one did
not complete the RCADS-25. As such, the TD sample consisted of 29 adolescents and
their parents.
Measures
Motor coordination difficulties. The Developmental Coordination Disorder
Questionnaire (DCDQ-07; Wilson et al., 2009) is a 15-item parent-report questionnaire
that measures motor coordination in children and adolescents (see Appendix B). It
consists of three subscales that measure control during movement, fine motor skills, and
general coordination. It provides a total score ranging from 15 to 75 with higher scores
indicating better motor coordination. The DCDQ-07 is commonly used as a screening
measure for DCD. In adolescents, a cut-off of 57 or below indicates the possible
presence of DCD. The DCDQ-07 has been found to have high internal consistency
(Cronbach’s alpha, α = .94), concurrent validity with performance-based measures of
motor ability (r = .55), and a good ability to detect DCD (sensitivity: 88.5%; specificity:
75.6%) (Wilson et al., 2009). In the current study, all parents were asked to complete the
DCDQ-07 to confirm group assignment and to obtain a measure of the severity of motor
difficulties in both study groups. Cronbach’s alpha for the DCDQ-07 Total score in the
current study was high (α = .98).
Internalising symptoms. The Revised Child Anxiety and Depression Scale –
Short Version (RCADS-25; Ebesutani et al., 2012) is a 25-item self-report questionnaire
22
that assesses depression (10 items) and anxiety (15 items) in children and adolescents
(see Appendix C). Adolescents are asked to rate how often they have been experiencing
difficulties on a four-point Likert-type scale from 0 (Never) to 3 (Always). The RCADS-
25 provides a total internalising symptoms score, in addition to separate subscale scores
for depression and anxiety. Raw scores are converted to age- and gender-standardised T-
scores based on normative reference groups (M = 50, SD = 10). T-scores of 65 or more
can be considered borderline clinically significant. The RCADS-25 has been found to
have acceptable internal reliability in both community (Anxiety, α = .94; Depression, α
= .79) and clinic-referred samples (Anxiety, α = .96; Depression, α = .80), and can
discriminate children with anxiety disorders and depression (Ebesutani et al., 2012). All
adolescents were asked to complete the RCADS-25 as a measure of internalising
symptoms. Cronbach’s alpha for the total score and the subscale scores in the current
study were high (Total, α = .92; Depression, α = .86; Anxiety, α = .90).
EF difficulties. The Behaviour Rating Inventory of Executive Function (BRIEF;
Gioia, Isquith, Guy, & Kenworthy, 2000) is an 86–item questionnaire that assesses EF
deficits in everyday life (see Appendix D). Parents are asked to rate their child’s
behaviour on a three-point Likert-type scale (‘Never a problem’, ‘Sometimes a
problem’, ‘Often a problem’). The BRIEF consists of eight clinical subscales that form
two composite indexes, the Behavioural Regulation Index (BRIEF BRI; i.e. inhibition,
shifting, emotional control) and the Metacognitive Index (BRIEF MCI; i.e. initiation,
working memory, planning, organisation of materials, monitoring). It also provides an
overall General Executive Composite (BRIEF GEC). Raw scores are converted to age-
and gender-standardised T-scores based on normative reference groups (M = 50, SD =
23
10). T-scores of 65 or more are suggested as the threshold for clinical significance
(Gioia et al., 2000). The BRIEF has been found to have high internal consistency (α =
.82-.98), test-retest reliability (r = .72-.84), and demonstrates predictive, convergent, and
divergent validity (Gioia et al., 2000). The Cronbach’s alpha for the BRIEF GEC and the
two subscale indexes in the present study were high (GEC, α = .98; BRI, α = .96; MCI, α
= .98).
Procedure
Advertisements for the study were distributed widely, as described in the
participants section (see Appendix E). This included via email, newsletters, social
media, and word of mouth. Interested participants were asked to read an information
sheet containing the study details (see Appendix F). Parents were asked to sign informed
consent whilst adolescents were asked to sign informed assent (see Appendices G and
H). Parents then completed an initial eligibility questionnaire (see Appendix I). Those
meeting criteria for the study were asked to complete the main questionnaires as part of
a survey. This included a section for the parent-report questionnaires and a section for
the adolescent self-report questionnaire. A survey containing the questionnaires was
available in paper form and online using Qualtrics survey software, depending on
participant preferences. At the end of the survey, participants were provided an
opportunity to enter a prize draw for a £100 Amazon voucher. The study received a
favourable ethical opinion from the University of Surrey Faculty of Health and Medical
Sciences Ethics Committee (see Appendix J).
24
Data analysis
Preliminary analyses. Data were analysed using IBM SPSS Statistics version
24. Scale and subscale scores were calculated for each of the questionnaire measures.
Missing data on the questionnaires were imputed using the mean of the available scores
for that scale. The data were screened for univariate outliers and parametric assumptions
within the DCD and TD groups separately. Homogeneity of variance was explored for
independent samples t-tests. Additionally, multivariate outliers, independence of errors,
linearity, homoscedasticity, normally distributed errors, homogeneity of regression, and
multicollinearity were explored for regression analyses. Descriptive statistics were
calculated to characterise the demographics for each group, with differences explored
using independent samples t-tests and chi-square tests. For each group, one-sample t-
tests were conducted to compare the RCADS-25 and BRIEF scores to the normative
samples for each measure.
Group comparisons. To test Hypotheses 1 and 2, internalising symptoms
(RCADS-25 Total) and EF difficulties (BRIEF GEC) were compared between the DCD
and TD groups using separate independent samples t-tests with alpha values set at .05.
Where parametric assumptions were not met, 95% bias-corrected and accelerated (BCa)
bootstrapped confidence intervals were calculated for the mean difference, based on
10,000 samples. If confidence intervals did not cross zero, then the difference can be
interpreted as significant. Based on guidelines, it was not deemed appropriate to adjust
for multiple comparisons since only a small number of pre-planned, specific hypotheses
were explored (Streiner & Norman, 2011). Instead, the exact p-values and confidence
intervals are reported to enable appropriate interpretation. Cohen’s d was also calculated
25
for each comparison as a measure of the effect size, whereby 0.3, 0.5 and 0.8 equate to
small, medium and large effect sizes respectively (Cohen, 1992).
Mediation analysis. A simple mediation analysis was conducted to test for an
indirect effect of DCD status on internalising symptoms through EF difficulties
(Hypothesis 3). DCD Status was dummy coded for these analyses (TD = 0, DCD = 1).
First, Pearson’s correlation coefficients were calculated to explore zero-order
correlations between all study variables and to determine whether demographics should
be included as covariates. 95% BCa bootstrap confidence intervals were calculated for
the correlation coefficients due to deviations from normality in some study variables.
The mediation analysis was then conducted using the PROCESS macro for SPSS
(Hayes, 2013). A bootstrapping approach was used based on 10,000 samples with
replacement, to calculate a 95% bias-corrected confidence interval for the indirect effect
(path ab; see Figure 1). If the confidence interval for the indirect effect does not cross
zero, then it can be considered significant. This approach makes no assumptions about
the sampling distribution of the indirect effect, increases power, minimises the risk of
Type II error, and is recommended for small samples (Fritz & MacKinnon, 2007;
Preacher & Hayes, 2004, 2008). The partially standardised effect size was calculated
which represents the number of standard deviations on the dependent variable (RCADS-
25 Total) by which the DCD and TD groups differ because of the indirect path. Given its
ease of interpretation, this measure is recommended for use in mediation analyses with a
dichotomous independent variable (Hayes, 2013; Lachowicz, Preacher, & Kelley, 2018).
Post-hoc analyses. Additional post-hoc analyses were conducted to better
understand the nature of any significant findings. This includes further independent
26
samples t-tests and mediation analyses using the subscales of the RCADS-25 and
BRIEF. These further analyses were exploratory to develop additional hypotheses and
therefore, based on guidelines, no adjustment for multiple testing was made (Streiner &
Norman, 2011). Again, p-values and confidence intervals are reported to enable
appropriate interpretation.
Power calculation
Based on previous research, a medium-large effect size (d = 0.6) was expected
for the group differences in internalising symptoms (Missiuna et al., 2014; see also Part
2) and a large effect (d = 0.8) for EF difficulties (Tal-Saban, Ornoy, & Parush, 2014; P.
H. Wilson et al., 2013). Power calculations, conducted using G Power v.3.1 (Faul,
Erdfelder, Lang, & Buchner, 2007) identified that a sample size of 90 would be required
to detect an effect size of 0.6 with 80% power and a 5% significance level. As such, the
study sample size of 43 was underpowered to detect a medium-large effect for
Hypotheses 1 and 2.
Power calculations for mediation analyses can be calculated based on the effect
size of path a and path b (Fritz & MacKinnon, 2007). As described above, a large effect
was expected for path a. A medium-large effect was also expected for path b, based on
previous research into the relationship of the BRIEF with internalising symptoms
(Ghassabian et al., 2014; White, Jarrett, & Ollendick, 2012). Fritz & MacKinnon (2007)
estimated that, for bias-corrected bootstrapping analyses, a minimum sample of 54 is
required to detect an indirect effect, with 80% power, when the effect of path a is large
27
and path b is medium (a conservative estimate). As such, the study sample size of 43
was slightly underpowered to detect the expected indirect effect.
Results
Preliminary analysis and descriptive statistics
The final sample consisted of 14 adolescents in the DCD group and 29
adolescents in the TD group. The BRIEF was missing a single item for three participants
which were imputed using the mean values of the available scores. The data were
screened for parametric assumptions (see Appendices K and L). No univariate or
multivariate outliers were identified. Both the RCADS-25 and BRIEF scores were
positively skewed in the TD group and negatively skewed in the DCD group.
Table 1. Summary of the demographics in the DCD and TD groups
Variable DCD
(n = 14)
TD
(n = 29)
Age, M (SD) years 13.84 (1.13) 13.72 (1.08)
Gender
Male, n (%) 9 (64.3%) 16 (55.2%)
Female, n (%) 5 (35.7%) 13 (44.8%)
DCDQ-07 Total, M (SD) 28.64 (8.54) 69.90 (4.86)
DCDQ-07 Control, M (SD) 12.50 (4.62) 28.10 (2.55)
DCDQ-07 Fine, M (SD) 7.71 (2.46) 18.17 (1.83)
DCDQ-07 General, M (SD) 8.43 (2.71) 22.93 (1.96)
DCD: Developmental Coordination Disorder; DCDQ-07: Developmental Coordination Disorder
Questionnaire – 07; TD: Typically developing
28
Table 1 summarises the descriptive statistics of the sample. Overall, there were
more males than females in the sample. There was a higher percentage of males in the
DCD group, however this difference was not significant, χ2 (1) = 3.22, p = 0.57. There
was also no significant difference in ages between the two groups, t (41) = -3.50; p =
0.74. Age and gender were, therefore, not included as covariates in group comparisons.
As expected, the DCD group had significantly lower total scores on the DCDQ-07, t
(41) = -20.23, p < .001, than the TD group.
The scores for the study measures are summarised in Table 2. Overall, the mean
total score on the RCADS-25 was lower in the TD group compared to the normative
sample and higher in the DCD group. One sample t-tests within each group found this
difference to be significant in the TD group, t (28) = -4.12, p < .001, but not significantly
different in the DCD group, t (13) = 0.69, p = .50. Within the TD group, one participant
(3.4%) scored above the clinical cut-off (T ≥ 65) for anxiety, but no participants scored
above cut-off for depression or overall internalising symptoms. Within the DCD group,
one participant (7.1%) scored above the clinical cut-off for depression, two for anxiety
(14.3%), and four (28.6%) for overall internalising symptoms.
The mean scores on the BRIEF GEC in the TD group were broadly comparable
with the normative samples, though the scores in the DCD group were higher. This
difference was significant in the DCD group, t (13) = 15.26, p = <.001, but not in the TD
group, t (27) = -2.01, p = .055. Only one participant (3.4%) scored above the clinical
cut-off (T ≥ 65) on the BRIEF GEC in the TD group. However, thirteen (93%) of the
DCD participants scored above the cut-off, indicating that the clear majority experienced
significant EF difficulties according to parent report.
29
Group differences
Independent samples t-tests were conducted to compare the two groups on
internalising symptoms (RCADS Total, Hypothesis 1) and EF difficulties (BRIEF GEC,
Hypothesis 2). Given that the distribution of the variables deviated from normality (see
Appendix K), bootstrapping with 10,000 samples was used to generate BCa 95%
confidence intervals for the mean difference.
Table 2. Summary of the scores for study variables
Variable DCD
(n = 14)
TD
(n = 29)
Mean
difference BCa 95% CI
RCADS-25 Total, M (SD) 52.23 (12.09) 41.98 (10.29) 10.24 2.96, 17.24*
RCADS-25 Depression, M (SD) 54.12 (9.64) 41.19 (9.33) 12.93 6.78, 18.78*
RCADS-25 Anxiety, M (SD) 50.49 (12.83) 44.19 (10.83) 6.30 -0.91, 13.64
BRIEF GEC, M (SD) 77.07 (6.64) 46.69 (8.80) 30.38 25.65, 34.77*
BRIEF BRI, M (SD) 75.36 (8.88) 48.28 (9.37) 27.08 21.42, 32.75*
BRIEF MCI, M (SD) 74.50 (7.21) 46.97 (9.13) 27.53 22.31, 32.44*
* 95% BCa bootstrapped confidence interval is significant
BCa: Bias-corrected and accelerated; BRI: Behavioural Regulation Index; BRIEF: Behaviour Rating
Inventory of Executive Function; CI: Confidence interval; DCD: Developmental Coordination Disorder;
GEC: Global Executive Composite; MCI: Metacognitive Index; RCADS-25: Revised Child Anxiety and
Depression Scale – Short version; TD: Typically developing
Internalising symptoms. Adolescents in the DCD group reported greater levels
of internalising symptoms (M = 52.23; SE = 3.23) compared to adolescents in the TD
group (M = 41.98; SE = 1.91). This difference, 10.24, BCa 95% CI [2.96, 17.24], was
significant, t (41) = 2.89, p = 0.006 and represents a large effect size, d = 0.90.
EF difficulties. Adolescents in the DCD group reported greater levels of EF
difficulties (M = 77.07; SE = 1.77) compared to adolescents in the TD group (M = 46.69;
30
SE = 1.63). This difference, 30.38, BCa 95% CI [25.65, 34.77]; p < .001) was
significant, t (41) = 11.42, p < .001 and represents a large effect size, d = 3.57.
Intercorrelations:
Intercorrelations between the study variables were computed using Pearson’s
correlation coefficients. Bootstrapped BCa 95% confidence intervals were calculated,
given the deviation from normality for some variables. There were significant
correlations between the independent, mediator and dependent variables as expected (see
Table 3). However, no significant correlation was identified between DCD status and the
RCADS-25 Anxiety subscale. Neither age nor gender were significantly correlated with
any of the study variables and were, therefore, not included as covariates in the
mediation analyses.
Mediation analysis
A simple mediation analysis was conducted to test each of the paths in the
mediation model. As shown in Figure 2 and Table 4, adolescents with a diagnosis of
DCD had higher levels of self-reported internalising symptoms, c = 10.24, p = .006, and
higher levels of parent-reported EF difficulties, a = 30.38, p <.001, compared to TD
adolescents. Adolescents with higher levels of parent-reported EF difficulties also self-
reported higher levels of internalising symptoms after controlling for DCD status, b =
0.55, p = .007. A bias-corrected (BC) bootstrap confidence interval for the indirect
effect, based on 10,000 bootstrap samples, did not cross zero, ab = 16.62, BC 95% CI
31
Table 3. Pearson correlation coefficients of variables with 95% bias-corrected and accelerated bootstrapped confidence intervals
* 95% BCa bootstrapped confidence interval is significant
BCa: Bias-corrected and accelerated; BRI: Behavioural Regulation Index; BRIEF: Behaviour Rating Inventory of Executive Function; CI: Confidence
interval; DCD: Developmental Coordination Disorder; GEC: Global Executive Composite; MCI: Metacognitive Index; RCADS-25: Revised Child Anxiety
and Depression Scale – Short version.
Variable 1 2 3 4 5 6 7 8
1. DCD status -
2. BRIEF GEC .87*
(.78, .94)
-
3. BRIEF BRI .82*
(.70, .90)
.93*
(.88, .97)
-
4. BRIEF MCI .84*
(.73, .92)
.96*
(.92, .99)
.83*
(.73, .90)
-
5. RCADS-25 Total .41*
(.10, .66)
.54*
(.33, .73)
.54*
(-.32, .73)
.49*
(.26, .69)
-
6. RCADS-25 Depression .55*
(.28, .77)
.62*
(.40, .79)
.63*
(.42, .80)
.57*
(.34, .75)
.86*
(.74, .94)
-
7. RCADS-25 Anxiety .25
(-.08, .55)
.40*
(.16, .63)
.40*
(.14, .64)
.36*
(.10, .60)
.94*
(.90, .97)
.64*
(.40, .82)
-
8. Age .06
(-.26, .38)
.15
(-.41, .17)
.07
(-.23, .36)
.16
(-.16, .47)
.02
(-.28, .33)
.07
(-.24, .39)
-.02
(-.29, .26)
-
9. Gender -.09
(-.36, .20)
.76
(-.33, .25)
-.02
(-.30, .28)
-.06
(-.35, .23)
.13
(-.16, .41)
.15
(-.15, .43)
.10
(-.20, .39)
-.11
(-.41, .17)
32
[4.10, 27.05]. The direct effect of DCD status on internalising symptoms was also no
longer significant after accounting for EF difficulties, c’ = -6.38, p = .346. The partially
standardised indirect effect was 1.41, BC 95% CI [0.30, 2.37]. These results indicate that
adolescents with DCD reported internalising symptoms that, on average, were 1.41
standard deviations (approximately 17 points on the RCADS-25) higher compared to TD
adolescents because of the indirect effect through parent-reported EF difficulties.
Table 4. Results of the mediation analysis using the RCADS-25 Total scores and BRIEF
GEC
* 95% bias-corrected bootstrapped confidence interval significant
BRIEF GEC: Behaviour Rating Inventory of Executive Function – Global Executive Composite; DV:
Dependent variable (RCADS-25); IV: Independent variable (group status); M: Mediator (BRIEF
GEC); RCADS-25: Revised Child Anxiety and Depression Scale – Short version.
Post-hoc analyses
Exploratory analyses were conducted using the subscales of the RCADS-25 and
BRIEF. Independent samples t-tests were conducted to compare the two groups. Given
that the distribution of the variables deviated from normality (see Appendix M),
bootstrapping with 10,000 samples was used to generate bias-corrected and accelerated
95% confidence intervals for the mean differences.
B
coefficient
SE t p-value Bias-corrected bootstrap
95% CI
Effect of IV on M (Path a) 30.38 2.66 11.42 <.001
Effect of M on DV (Path b) 0.55 0.19 2.85 .007
Total Effect (Path c) 10.24 3.54 2.89 .006
Direct effect (Path c’) -6.38 6.69 -0.95 .346
Indirect Effect (a x b) 16.62 [4.16, 27.04]*
33
Figure 2. Results of the mediation analysis using the RCADS-25 Total scores and
BRIEF GEC
RCADS-25 subscales. On the RCADS-25, adolescents in the DCD group
reported greater levels of depression (M = 54.12; SE = 2.58) compared to adolescents in
the TD group (M = 41.19; SE = 1.73). This difference, 12.93, BCa 95% CI [6.78, 18.78],
was significant, t (41) = 4.21, p < .001, and represents a large effect size, d = 1.32.
Adolescents in the DCD group also reported greater levels of anxiety (M = 50.49; SE =
3.43) compared to adolescents in the TD group (M = 44.19; SE = 2.01). This difference,
6.30, BCa 95% CI [-0.91, 13.64], was not significant t (41) = 1.68, p = .100. However, it
did represent a medium effect size (d = 0.52).
BRIEF subscales. On the BRIEF, adolescents in the DCD group had greater
levels of parent-reported behavioural regulation difficulties (M = 75.36; SE = 2.37)
compared to adolescents in the TD group (M = 48.28; SE = 1.74). This difference, 27.08,
BCa 95% CI [21.42, 32.75], was significant, t (41) = 9.03, p < .001, and represents a
34
large effect size, d = 2.82. Adolescents in the DCD group also had greater levels of
parent-reported metacognitive difficulties (M = 74.50; SE = 1.93) compared to
adolescents in the TD group (M = 46.99; SE = 1.70). This difference, 27.53, BCa 95%
CI [22.31, 32.44], was significant t(41) = 9.87, p < .001, and represents a large effect
size (d = 3.08).
Subscale mediator models. Two parallel multiple mediation models were
conducted to explore the relationship between DCD status and each subscale of the
RCADS-25 (Depression and Anxiety) separately. For both models, the separate
subscales on the BRIEF (BRIEF BRI and BRIEF MCI) were included as parallel
mediators (path ab1 and ab2, respectively). This allowed further exploration of the
potential paths through which EF difficulties mediate the relationship between DCD and
internalising symptoms. The relevant assumptions were confirmed for each model prior
to analysis (see Appendix N). The results are summarised in Table 5.
Depression symptoms: A parallel multiple mediation model was conducted to
explore the effect of DCD status on depression through both behavioural regulation
difficulties and metacognitive difficulties. Bias-corrected bootstrap confidence intervals
for the indirect effects, based on 10,000 bootstrap samples, found a significant indirect
effect of behavioural regulation difficulties, a1 = 9.77, 95% CI [1.81, 17.74], but not
metacognitive difficulties, a2 = 2.05, 95% CI [-8.59, 12.87]. The partially standardised
indirect effect through behavioural regulation difficulties was 0.88, BC 95% CI [0.12,
1.56]. The findings did not change when investigating the mediators independently in
two simple mediation models.
35
Anxiety symptoms: Although no significant difference between the two groups in
levels of anxiety symptoms was identified, evidence of an association between the
independent and dependent variables is not a requirement for mediation (Zhao, Lynch,
& Chen, 2010). Therefore, a parallel multiple mediation model was also conducted to
explore the effect of DCD status on anxiety through both behavioural regulation
difficulties and metacognitive difficulties. Bias-corrected bootstrap confidence intervals
for the indirect effects, based on 10,000 bootstrap samples, crossed zero for both
behavioural regulation difficulties, a1 = 8.84, 95% CI [-3.09, 20.48] and metacognitive
difficulties, a2 = 6.07, 95% CI [-8.82, 21.84], suggesting no significant indirect effect.
Table 5. Results of the parallel multiple mediation models using the subscales of the
BRIEF and RCADS-25
B
coefficient
SE t p-value Bias-corrected bootstrap
95% CI
DV: RCADS-25 Depression
Path a1: IV-M1 27.08 3.00 9.03 <.001
Path b1: M1-DV 0.36 0.17 2.13 .040
Path a2: IV-M2 27.53 2.79 9.87 <.001
Path b2: M2-DV 0.07 0.18 0.41 .686
Path c: Total Effect 12.93 3.07 4.21 <.001
Path c’: Direct effect 1.11 5.81 0.19 .849
a1b1: Indirect effect 9.77 [1.81, 17.74]*
a2b2: Indirect effect 2.05 [-8.59, 12.87]
DV: RCADS-25 Anxiety
Path a1: IV-M1 27.08 3.00 9.03 <.001
Path b1: M1-DV 0.33 0.21 1.56 .126
Path a2: IV-M2 27.53 2.79 9.87 <.001
Path b2: M2-DV 0.22 0.22 0.98 .333
Path c: Total Effect 6.30 3.74 1.68 .100
Path c’: Direct effect -8.61 7.15 -1.20 .236
a1b1: Indirect effect 8.84 [-3.09, 20.48]
a2b2: Indirect effect 6.07 [-8.82, 21.84]
* 95% bias-corrected bootstrapped confidence interval significant
36
BRIEF: Behaviour Rating Inventory of Executive Function; DV: Dependent variable; IV:
Independent variable (group status); M1: Mediator (BRIEF Behaviour Regulation Index); M2:
Mediator (BRIEF Metacognitive Index); RCADS-25: Revised Child Anxiety and Depression Scale –
Short version.
TD sample. Due to the small sample in the DCD group and the potential
heterogeneity between the two groups due to differing sampling strategies, the mediation
analysis was repeated in the TD group only (see Table 6). For this model, the total score
on the DCDQ-07 was used as a continuous independent variable. The three TD
participants excluded from the main analysis due to scoring below the cut-off on the
DCDQ-07 were included in this analysis (n = 32; see Appendix O for exploration of
assumptions). The results found that poorer motor coordination in TD adolescents was
associated with higher levels of self-reported internalising symptoms, c = -0.53, p =
.028, and higher levels of parent-reported EF difficulties, a = -0.66, p <.001. TD
adolescents with higher levels of parent-reported EF difficulties also self-reported higher
levels of internalising symptoms after controlling for motor coordination, b = 0.71, p =
.001. A bias-corrected bootstrap confidence interval for the indirect effect, based on
10,000 bootstrap samples, did not cross zero, ab = -0.47, BC 95% CI [-0.84, -0.16]. The
direct effect of motor coordination on internalising symptoms was also no longer
significant after accounting for EF difficulties, c’ = -0.06, p = .787. The completely
standardised indirect effect was -0.34, 95% BC CI [-0.57, -0.13]. These results indicate
that, in TD adolescents, a decrease of one standard deviation in motor coordination skills
is associated with, on average, an increase of 0.34 standard deviations in self-report
internalising symptoms because of the indirect effect through parent-reported EF
difficulties.
37
Table 6. Results of the mediation analysis based on the TD group only
* 95% bias-corrected bootstrapped confidence interval significant
BRIEF: Behaviour Rating Inventory of Executive Function; DV: Dependent variable (Revised Child
Anxiety and Depression Scale – Short version); IV: Independent variable (Developmental Coordination
Disorder Questionnaire – 07 Total Score); M: Mediator (Behaviour Rating Inventory of Executive
Function).
Discussion
The aim of this study was to investigate internalising symptoms and EF
difficulties in adolescents with and without DCD. As hypothesised, adolescents with
DCD had greater levels of self-reported internalising symptoms (Hypothesis 1) and
greater levels of parent-reported EF difficulties (Hypothesis 2) compared to TD
adolescents. The results also identified that parent-reported EF difficulties mediated the
relationship between DCD status and internalising symptoms (Hypothesis 3). Further
exploratory analyses identified that the difference in internalising symptoms between the
two groups was greatest for symptoms of depression and that this effect was mediated
by behavioural regulation difficulties, but not metacognitive difficulties.
Internalising symptoms in DCD
The findings replicate previous research identifying that individuals with DCD
experience greater levels of internalising symptoms than their TD peers (Mancini et al.,
2016; Missiuna & Campbell, 2014, see Part 2 for a review). More specifically, the
B
coefficient
SE t p-value Bias-corrected bootstrap
95% CI
Effect of IV on M (Path a) -0.66 0.18 -3.60 .001
Effect of M on DV (Path b) 0.71 0.19 3.70 .001
Total Effect (Path c) -0.53 0.23 -2.31 .028
Direct effect (Path c’) -0.06 0.23 -0.27 .787
Indirect Effect (a x b) -0.47 [-0.84, -0.16]*
38
findings are consistent with the few existing studies that have investigated internalising
symptoms in adolescents with the disorder (Harrowell et al., 2017; Li et al., 2018;
Skinner & Piek, 2001; Wagner et al., 2016). The magnitude of this effect was also large,
with adolescents in the DCD group scoring almost one standard deviation higher on self-
reported internalising symptoms compared to the TD adolescents. This difference can be
considered clinically significant (Norman, Sloan, & Wyrwich, 2003) and would equate
to the adolescents with DCD reporting one point higher on at least ten items of the
RCADS-25.
However, the magnitude of the difference in the present study was greater than
might be expected based on past research, since meta-analytic findings suggest the
difference to be around half a standard deviation (see Part 2). It is likely that the effect in
the present study was inflated due to the use of convenience sampling, which has been
found to result in greater effect sizes (Crane, Sumner, & Hill, 2017; Hill & Brown, 2013;
Pratt & Hill, 2011; Wagner, Bos, Jascenoka, Jekauc, & Petermann, 2012; Watson &
Knott, 2006) compared to studies using a population-based screening strategy (Campbell
et al., 2012; Francis & Piek, 2003; Harrowell et al., 2017; Missiuna et al., 2014; Skinner
& Piek, 2001; Wagner et al., 2016). Indeed, the TD group in the present study reported
significantly lower internalising symptoms than the normative population (Chorpita,
Moffitt, & Gray, 2005) with no participants scoring above the clinical threshold,
suggesting it was an unrepresentative sample. Despite the potentially inflated effect size,
the direction of the effect is consistent with higher quality studies suggesting individuals
with DCD experience greater levels of internalising symptoms than their TD peers
(Harrowell et al., 2017; Wagner et al., 2016).
39
These findings are in line with the growing consensus that the impact of DCD
extends beyond the core motor difficulties that characterise the disorder and includes
significant implications for the mental health of those affected. The environmental-stress
hypothesis (Cairney et al., 2013) would suggest that the motor difficulties experienced
by the DCD group impacts on their mental health indirectly through a variety of
secondary psychosocial stressors. Although these stressors were not measured in the
present study, they might include increased peer victimisation (Campbell et al., 2012),
reduced leisure activities (Raz-Silbiger et al., 2015), poorer self-esteem (Rigoli, Piek, &
Kane, 2012), physical inactivity (Li et al., 2018), reduced social support (Rigoli et al.,
2017), and lower perceived academic performance (Lingam et al., 2012).
Interestingly, the findings revealed that the two groups differed significantly on
symptoms of depression but not anxiety. This contradicts previous research that has
found DCD to impact on specific measures of both depression (Campbell et al., 2012;
Francis & Piek, 2003; Harrowell et al., 2017; Hill & Brown, 2013; Missiuna et al., 2014;
Piek et al., 2007; Watson & Knott, 2006) and anxiety (Hill & Brown, 2013; Missiuna et
al., 2014; Pratt & Hill, 2011; Schoemaker & Kalverboer, 1994). The failure to detect a
difference in anxiety symptoms likely reflects insufficient power in the present study,
since a medium effect size was still found. However, these preliminary findings do
suggest that the impact of DCD on internalising symptoms in adolescents may be greater
for depressive symptoms than anxiety symptoms. Indeed, Missiuna et al. (2014) reported
a greater effect size for self-reported depressive symptoms than for self-reported anxiety
symptoms in adolescents with DCD compared to their TD peers. This suggestion would
fit with findings that some of the secondary psychosocial stressors proposed in the
40
environmental-stress hypothesis are more often linked with depression than they are
with anxiety, including reduced self-esteem (Sowislo & Orth, 2013) and peer
victimisation (Hawker & Boulton, 2000).
EF difficulties in DCD
The present findings are also consistent with previous research highlighting EF
deficits in DCD (Alloway, 2007; Bernardi et al., 2018; Leonard & Hill, 2015; Mandich
et al., 2002; P. H. Wilson et al., 2013; Wuang et al., 2011). The DCD group was found
to have significantly higher levels of EF difficulties for both behavioural regulation and
metacognitive functions. This is in line with past research highlighting difficulties for
people with DCD across a wide range of EF task, including inhibition, cognitive
flexibility, working memory and planning (Leonard & Hill, 2015). These difficulties can
be understood through the shared underlying neurological mechanisms for both motor
skills and EFs, which include the prefrontal cortex and cerebellum (Diamond, 2000). As
such, the underdevelopment of motor skills that characterise DCD are closely
interrelated with the EF deficits (Koziol et al., 2012; Rigoli, Piek, Kane, & Oosterlaan,
2012).
This study is also the first to identify EF difficulties in adolescents with DCD
using a behaviour rating scale of EF. This suggests that the EF deficits observed on
performance-based measures in adolescents with DCD also generalises to EF difficulties
in everyday life, supporting similar findings in an adult sample (Tal Saban et al., 2014).
The effect size in the present study was also very large, with parent-reported EF
difficulties in the DCD group being over 3 standard deviations higher than in the TD
41
group. Although a large effect was expected based on past research (Tal Saban et al.,
2014; P. H. Wilson et al., 2013), the magnitude was even greater in the present study. It
is again possible that the effect was inflated due to design limitations, especially the use
of a convenience sampling strategy. However, these preliminary findings might suggest
that the EF difficulties experienced by adolescents with DCD may be even more marked
in day-to-day life than has been previously identified on highly structured, laboratory-
based tasks.
Internalising symptoms in DCD are mediated by EF difficulties
A notable finding in the present study is that the elevated internalising symptoms
in adolescents with DCD, compared to their TD peers, was mediated by EF difficulties.
This is consistent with expectations, given evidence that EF deficits are associated with
mental health difficulties (Evans et al., 2016, 2016; Han et al., 2016; Lengua, 2006;
Letkiewicz et al., 2014; Martel et al., 2007; Nigg et al., 1999; Riggs et al., 2003). This
mediating effect also sits alongside the findings of research with other childhood
disorders that impact on both EFs and internalising symptoms (Kelly et al., 2012;
Lawson et al., 2015). Research has identified that EFs are important for the effective use
of appropriate emotion regulation strategies (Joormann & D’Avanzato, 2010;
Schmeichel & Tang, 2015). It is possible that the EF impairments in the adolescents
with DCD contributed to an increased use of maladaptive emotion regulation strategies
such as rumination (Demeyer et al., 2012; Johnson, 2009; Meiran et al., 2011), worry
(Brosschot et al., 2006) and withdrawal (Wante et al., 2017), and a reduced use of
adaptive strategies such as reappraisal (Joormann & Gotlib, 2010) and distraction
42
(Wante et al., 2017). This, in turn, may have contributed to increased levels of
internalising symptoms. EF deficits may also have impacted on other areas of
functioning, including academic performance (Best et al., 2011) and social functioning
(Dawson et al., 2012), which may have contributed to elevated internalising symptoms
(Ende et al., 2016; Nilsen et al., 2013; Zhang et al., 2018).
It is also of note that, after accounting for the indirect effect through EF
difficulties, the direct effect of DCD on internalising symptoms was no longer
significant. Additionally, the effect size of the mediation analysis indicated that the
adolescents with DCD reported internalising symptoms that were over one standard
deviation higher, compared to TD adolescents, due to the indirect effect through EF
difficulties. This highlights that the role of EF deficits in explaining internalising
symptoms in DCD may be a major one. Yet previous attempts to explain the increased
risk of internalising symptoms in DCD (i.e. the environmental-stress hypothesis) have
failed to include these higher-order cognitive abilities in their model (Cairney et al.,
2013; Mancini et al., 2016). The environmental-stress hypothesis may benefit from the
inclusion of EFs as another mediating factor between DCD and internalising symptoms.
This might be through previously untested pathways, including its impact on emotion
regulation, academic functioning or social skills. Additionally, it is possible that EFs
may moderate and mediate the other identified pathways in the model. For example, EFs
may influence self-perceptions (Hughes & Ensor, 2011), social support (Beauchamp &
Anderson, 2010) and resilience against peer victimisation (Agoston & Rudolph, 2016).
Exploratory analyses identified that the indirect effect can be best explained as
DCD impacting on depressive symptoms through behavioural regulation difficulties. No
43
indirect effect was found for depression through metacognitive difficulties. Additionally,
no indirect effect was found for anxiety through either type of EF. The failure to find an
indirect effect through these other paths could be due to insufficient power in the present
study, since only a medium-large indirect effect could be detected with the sample size.
However, the results would suggest that difficulties in behavioural regulation may be
most pertinent to the mental health difficulties in DCD, especially depression. To some
extent, these findings would fit with the proposed explanation that emotion regulation
deficits underlie the link between EF difficulties and internalising symptoms. This is
because the BRI on the BRIEF measures a person’s ability to shift and modulate
behaviours and emotions via appropriate inhibitory control (Gioia et al., 2000).
Emotional control is a key aspect of the BRI, as is inhibition and cognitive flexibility
which have been implicated in emotion regulation strategies (Demeyer et al., 2012;
Johnson, 2009; Joormann & Gotlib, 2010; Meiran et al., 2011). The MCI, on the other
hand, measures a person’s cognitive ability to problem-solve, monitor performance and
self-manage tasks. There is generally less research linking these metacognitive abilities
to emotion regulation. Instead, metacognitive abilities may be important for more
practical and social skills (Gilotty, Kenworthy, Sirian, Black, & Wagner, 2002; Pugliese
et al., 2015). Consistent with this, Gardiner and Iarocci (2018) found that behavioural
regulation difficulties predicted depressive symptoms in adolescents, whereas
metacognitive difficulties were a better predictor of daily living skills, communication
skills and socialisation abilities. It is, therefore, a plausible finding that deficits in EFs
related to behavioural regulation are most important in explaining the link between DCD
and internalising symptoms, particularly depression.
44
Finally, EFs were also found to mediate the relationship between motor
difficulties and internalising symptoms in the TD adolescents. This is consistent with the
emerging literature investigating motor difficulties as a dimensional construct in
community samples, including its relationship with internalising symptoms (Piek et al.,
2010; Poole et al., 2015; Sigurdsson E et al., 2002) and EF difficulties (Rigoli, Piek,
Kane, et al., 2012). This would suggest that subclinical symptoms of DCD, and motor
difficulties in general, can impact on internalising symptoms and that this may also be
mediated by EF difficulties. This finding also provides extra support for the main results
of this study. It suggests that the findings cannot be explained solely by the potential
bias arising through the unrepresentativeness of the TD sample.
Strengths and Limitations
There are several limitations in the present study and so the results should be
interpreted with caution. Given the cross-sectional design, it is not possible to establish
causality in the relationships identified. Although prior longitudinal research suggests
that DCD predicts both EF difficulties and internalising symptoms, and that EF
difficulties predict internalising symptoms, these directional relationships could not be
confirmed in the present study. For example, there is evidence that internalising
symptoms can exacerbate EF difficulties (Vilgis, Silk, & Vance, 2015). Alternatively,
the relationship between variables might be better explained by their shared associations
with another untested variable.
Despite attempts to recruit participants across a wide range of sources, the
response rate in both the DCD and TD groups was very low. This resulted in a small
45
sample size with insufficient power to detect medium effect sizes. As such,
interpretations could only be made about the larger effects and are somewhat tentative.
The low response rate, and the use of a convenience sampling strategy, also raises the
question of how representative the sample was of the populations studied. It is possible
that only a certain subgroup of parents and adolescents volunteered to participate in the
study. In the DCD group, this may have included parents and adolescents who were
closely involved with the organisations that aided in advertising the study. Given the
supportive nature of these organisations, these volunteers may benefit from greater
protective resources than those with no links to such support. Indeed, the internalising
symptoms in the DCD group were not found to differ significantly from the normative
population, suggesting the difficulties in mental health were less apparent than might be
expected in the DCD population. On the contrary, internalising symptoms in the TD
group were significantly lower than the normative population, suggesting the sample
was unrepresentative. The use of a convenience sampling strategy likely provided less
accurate estimates of the effects compared to a population screening strategy.
Although the two groups did not differ significantly in age and gender, and the
results did not change when controlling for these confounders, other untested
confounders may have influenced the results. For example, socioeconomic status (SES)
was not measured, though it has been linked to both internalising symptoms
(Letourneau, Duffett-Leger, Levac, Watson, & Young-Morris, 2013) and EFs (Hackman
& Farah, 2009). However, the reported effects of SES are small and inconclusive (Gioia
et al., 2000; Twenge & Nolen-Hoeksema, 2002). Other factors that could potentially be
important are maternal depression (Harrowell et al., 2017), ethnicity (Twenge & Nolen-
46
Hoeksema, 2002) and IQ (Lingam et al., 2012), though the use of IQ as a covariate in
studies investigating neurodevelopmental disorders is controversial (Dennis et al., 2009).
These potential confounding factors often go unmeasured in research into DCD since
recruitment is often challenging and the primary measures take priority. Additionally,
although adolescents with comorbid disorders were excluded based on self-reported
diagnoses, it is also unclear to what extent undiagnosed difficulties or subclinical
symptoms of ADHD or ASD could have contributed to the findings.
Another limitation is that internalising symptoms were based only on self-report
and EF difficulties on parent-report. Although clinical cut-offs could be used, only
diagnostic interviews could establish the rates of psychiatric diagnoses in each group.
Additionally, behaviour rating scales of EF only correlate modestly with performance-
based measures of EF. It is, therefore, unclear if similar findings would be found using
more structured, controlled measures of EF. Related to this, the present study relied on
parent-report and a screening measure to rule out a diagnosis of DCD in the TD group.
A more rigorous, independent assessment based on performance-based measures and a
clear developmental history would be more accurate. This is especially important given
that DCD is often undiagnosed (Gaines et al., 2008), placing greater needs on
researchers to assess this independently.
However, this is the first study to investigate whether difficulties in EFs mediate
the relationship between DCD and internalising symptoms. This is an important factor
that has not been included in previous explanations for this relationship (Cairney et al.,
2013; Mancini et al., 2016). It is also the first study to investigate everyday EF
difficulties in adolescents with DCD compared to their TD peers. The use of different
47
respondents for the mediator and dependent variables minimises common method bias
which is often a major limitation among studies investigating mediation models.
Generally, the effect sizes were also of a large magnitude, suggesting that further
exploration of these relationships in future research could have important theoretical and
clinical implications.
Clinical implications
These findings echo previous research indicating that the impact of DCD extends
beyond the motor difficulties that characterise the disorder. They highlight the need for
healthcare and education professionals to become more aware of the impact the disorder
has on both internalising symptoms and on EF. This is especially important given that
the condition is poorly understood among professionals (Gaines et al., 2008; B. N.
Wilson et al., 2013) and given the difficulties families report in obtaining the right
support (Stephenson & Chesson, 2008). It suggests that individuals with DCD would
benefit from further assessment of their EF abilities and appropriate support with this in
both education and healthcare settings. Indeed, individuals diagnosed with DCD in
adulthood have highlighted their EF difficulties as being amongst their main concerns
and reasons for seeking support, as opposed to the motor difficulties itself (Purcell,
Scott-Roberts, & Kirby, 2015). The findings also support the practice of routine
screening of mental health difficulties in individuals with DCD to identify potentially
undiagnosed comorbid difficulties, especially depression. Given the numerous pathways
through which DCD might impact on internalising symptoms (Mancini et al., 2016),
these suggestions would require close collaboration among teachers, educational
48
psychologists, occupational therapists, medical practitioners, social workers and mental
health professionals to meet an individual’s needs holistically.
The findings also suggest that EF deficits may play a key role in the increased
risk of internalising symptoms in people with DCD. Given that research has found
interventions can improve EFs if targeted during childhood (Diamond & Lee, 2011), this
provides an important area of treatment for individuals with DCD and comorbid mental
health difficulties. Although the findings are only preliminary, it would suggest that this
may be most important for depressive symptoms in adolescents with DCD. It also
suggests that a focus on behavioural regulation strategies may be most effective. This
might include learning to shift attention away from negative emotional stimuli (e.g.
negative thoughts), inhibit negative behavioural and emotional responses, and develop
more effective emotion regulation strategies. The findings would also suggest that, for
mental health professionals presented with a client with DCD and comorbid depression,
it would be helpful to be aware of these behavioural regulation difficulties and perhaps
consider them as part of their intervention. For example, there is some suggestion that
third-wave cognitive-behavioural models may improve behavioural regulation, including
elements of mindfulness training (Flook et al., 2010), promoting psychological
flexibility (Whiting, Deane, Simpson, McLeod, & Ciarrochi, 2017), and developing
emotion regulation strategies (McMain, Korman, & Dimeff, 2001). On the contrary,
attempts to improve metacognitive skills such as problem-solving, planning and
organisation may be less helpful.
49
Future research
Given the limitations of the present study, further research is needed to support
the current findings. Longitudinal studies, controlling for the stability of EF difficulties
and internalising symptoms over time, are necessary to better understand the causal
pathways linking DCD, EFs, and internalising symptoms. Future research could also
explore the specific pathways through which EF difficulties lead to internalising
symptoms in DCD. This might include indirect effects through emotion regulation
strategies and through the existing pathways suggested in the environmental stress
hypothesis (e.g. peer victimisation, social support, self-esteem). More complex
analytical techniques, such as structural equation modelling, could provide further
insight into the complexity of the relationships between these variables. These future
studies should also adopt large-scale, population-based screening strategies controlling
for a range of potential confounders to maximise the quality of their findings. The
addition of performance-based measures of various EFs would also allow for more in-
depth analyses into the specific EF abilities that are important in these relationships. It
would also be important to replicate findings across the age groups, including younger
children and adults. Additionally, there is a need for intervention studies to determine
whether targeting EF deficits in DCD can improve the mental health of this population.
Conclusion
This study supports the findings of previous research indicating that adolescents
with DCD experience greater levels of internalising symptoms and EF difficulties
compared to their TD peers. It is also the first study to identify EF difficulties as a key
50
explanatory factor in the link between DCD and mental health problems. Although these
findings are considered preliminary, it suggests that EF difficulties could be an
important addition to previous attempts at conceptualising the elevated internalising
symptoms in this population (Cairney et al., 2013; Mancini et al., 2016). It also
highlights EFs as a potential intervention target for improving the emotional wellbeing
of adolescents with DCD. However, further research is needed to support these findings.
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List of appendices
Appendix A: Guidelines for authors 71
Appendix B: Developmental Coordination Disorder Questionnaire – 07 (DCDQ-
07)
72
Appendix C: Revised Child Anxiety and Depression Scale – Short version
(RCADS-25)
73
Appendix D: Behaviour Rating Inventory of Executive Function (BRIEF) 74
Appendix E: Study advertisement 75
Appendix F: Information sheets 77
Appendix G: Parent consent forms 90
Appendix H: Adolescent assent forms 93
Appendix I: Eligibility screening questionnaire 95
Appendix J: Favourable ethical opinion 96
Appendix K: Assumptions for independent samples t-tests 97
Appendix L: Assumptions for simple mediation analysis 102
Appendix M: Assumptions for subscale analyses using independent samples t-
tests
107
Appendix N: Assumptions for parallel multiple mediation analysis based on
subscales
114
Appendix O: Assumptions for simple mediation analysis within the TD sample 117
71
Appendix A: Guidelines for authors
[Appendix removed for E-Thesis submission]
72
Appendix B: Developmental Coordination Disorder Questionnaire – 07 (DCDQ-07)
[Appendix removed for E-Thesis submission]
73
Appendix C: Revised Child Anxiety and Depression Scale – Short version
(RCADS-25)
[Appendix removed for E-Thesis submission]
74
Appendix D: Behaviour Rating Inventory of Executive Function (BRIEF)
[Appendix removed for E-Thesis submission]
75
Appendix E: Study advertisements
A copy of the advertisement distributed for participants with DCD is displayed below:
University of Surrey research
We are researchers at the University of Surrey looking to understand the mental health and thinking abilities in adolescents with and without Developmental Coordination
Disorder (also known as Dyspraxia).
In this study, we will ask parents to complete some questionnaires about their child’s motor ability and thinking abilities (e.g. planning and memory). Your child will also be asked to complete a questionnaire about their mental health.
Your child can take part if he/she is aged between 12 and 15 and has a diagnosis of Developmental Coordination Disorder / Dyspraxia. All your responses will be anonymous and you will be given the chance to enter a raffle to win a £100 Amazon voucher!
If interested, please email Serif at [email protected] for more information.
This study has received a favourable ethical opinion from the Faculty of Health and Medical
Sciences Ethics Committee, at the University of Surrey
76
A copy of the advertisement distributed for TD participants is displayed below:
University of Surrey research
Hi! My name is Serif Omer. We are conducting a research project to find out more about the link between motor coordination, thinking skills, and mental health. As part of this project, we are looking for young people (age 12-15) and their parents/guardians to complete some brief online questionnaires. They take about 15 minutes for parents/guardians and 5 minutes for the young person. All your responses will be anonymous and you will be given the chance to enter a raffle to win a £100 Amazon voucher! Please visit the following web link to access the survey: https://surreyfahs.eu.qualtrics.com/jfe/form/SV_a2wl5KRUw0vNXX7 Paper copies can also be provided. Please feel free to contact me if you have any questions: [email protected]. Thank you very much!
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Appendix F: Information sheets
Separate information sheets were produced for parents and adolescents in each study
group. Copies of these information sheets are provided on the following pages.
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Parent Information Sheet (DCD group; 07.11.2017; Version 2) Title of Project
Executive function and internalizing problems in adolescents with and without Developmental Coordination Disorder Introduction
We would like to invite you and your child to take part in a research project. Before you and your child decide to take part, you need to understand why the research is being done and what it will involve. Please take the time to read the following information carefully. Talk to others about the study if you wish. This study is being conducted by Serif Omer (Trainee Clinical Psychologist), under the supervision of Dr Hayley Leonard (Lecturer in Developmental Psychology and Neurodevelopmental Disorders). Please ask questions if there is anything you do not understand. What is the purpose of the study? We know that adolescents with Developmental Coordination Disorder (DCD; sometimes also called ‘Dyspraxia’) often have difficulties with high-level thinking abilities, such as planning and memory. They also often report increased symptoms of anxiety and depression compared to others their age without the disorder. The current project aims to investigate this further by understanding how these difficulties may be related to each other. Why have I been invited to take part in the study? As part of this study, we are seeking adolescents (between the age of 12 and 16) with a diagnosis of DCD / dyspraxia and one of their parents/guardians. You and your child have been invited to take part because you might meet these criteria. Do I have to take part? No, neither you nor your child has to participate. There will be no adverse consequences if you decide not to participate. You can also withdraw your participation at any time without giving a reason.
79
What will my involvement require?
As the child’s parent or guardian, you will be asked to complete a consent form. You will then be asked a set of questions. These can be completed online, by post, over the phone, or face-to-face if we visit you at home. This should take no more than 30 minutes in total and will include questions about your child’s movement abilities (such as sports skills, handwriting, etc.) and their high-level thinking skills (such as planning and memory). You will also be asked to provide a copy of the clinical report confirming your child’s diagnosis of DCD. This will be checked by the research team to ensure your child is eligible and any relevant scores on diagnostic tests will be recorded. You will not receive any payment for taking part. You will be given the option at the end of the survey to enter a prize draw for a £100 Amazon voucher. The winner will be contacted by email at the end of study in April 2018. What will my child’s involvement require?
If you consent for your child to take part and they are suitable for the study, then they will be asked to independently complete a questionnaire concerning their moods and emotions. It should take approximately 10 minutes and can be completed online, over the phone, or on paper. Your child will not receive any payment for taking part. What will I have to do?
If you and your child would like to take part, please contact the research team on [email protected] (Serif Omer) or using the contact details below. A researcher will then be in contact to obtain consent and administer the questionnaires. Please feel free to contact the research team if you have any questions. What are the possible disadvantages or risks of taking part?
There is a possibility that some of the questions may highlight sensitive issues for you or your child. If you want to talk about the questions or your answers, please contact the research team. If your child appears to experience any distress, the session will be terminated immediately and the research team will alert you. What are the possible benefits of taking part? It is unlikely that you or your child will benefit directly from taking part. However, it is hoped that the study will improve our understanding of mental health and
80
thinking abilities in people with motor coordination difficulties, which could have clinical implications for improving the lives of this group of people. What happens when the research study stops?
You may receive a summary of the research findings at the end of the study (after February 2018). You can indicate if and how you would like to receive this on the initial screening questionnaire. This summary will only include the overall findings of the study. We will not provide individual feedback on your child’s or your own responses. What if there is a problem? Any complaint or concern about any aspect of the way you have been dealt with during the course of the study will be addressed; please contact Dr Hayley Leonard (Research Supervisor) on 01483 686888 or [email protected]. You may also contact the Head of School, Professor Derek Moore, on 01483 686933 or [email protected]. Will taking part in the study be kept confidential? Yes. All of the information that you and your child give will be anonymised so that those reading reports from the research will not know who has contributed to it. All project data will be held for at least 6 years and all research data for at least 10 years in accordance with University policy. Data will be stored securely in accordance with the Data Protection Act 1998. However, should you or your child disclose information that suggests your child is at risk then the researcher may need to report this to an appropriate authority. This would usually be discussed with you first. Contact details
Serif Omer Dr Hayley Leonard Trainee Clinical Psychologist Lecturer School of Psychology School of Psychology AD Building AD Building University of Surrey University of Surrey Guildford Guildford GU2 7XH GU2 7XH [email protected] [email protected] 01483 686888 Who is organising and funding the research?
81
This research is unfunded and is being completed by Serif Omer as part of a Doctorate in Clinical Psychology at the University of Surrey. Who has reviewed the project?
The study has been reviewed and received a Favourable Ethical Opinion (FEO) from the Faculty of Health and Medical Sciences Ethics Committee, at the University of Surrey. Thank you for taking the time to read this Information Sheet.
82
Adolescent Information Sheet (DCD group; 17.11.17; Version 2)
Title of Project
Executive function and internalizing problems in adolescents with and without
Developmental Coordination Disorder
Introduction
Hi, my name is Serif Omer and I would like to invite you to take part in a research study.
At the University of Surrey, we are trying to learn more about the effect of
Developmental Coordination Disorder on young people. People with Developmental
Coordination Disorder (DCD), which is sometimes called ‘Dyspraxia’, have difficulties
with movement tasks (such as handwriting and sports). However, they may also have
difficulties with their mood and some thinking skills (such as memory and planning
ahead). We would like to know more about whether young people with DCD have
differences in their mood and thinking skills compared to young people without DCD and
why this might be.
Why is this study being done?
We hope that this research will help to better understand the effect of DCD/dyspraxia
on young people which could help to improve their lives. This research could also help to
better understand difficulties with mood and thinking skills in young people that do not
have DCD.
Why have I been invited to take part? As part of this study, we are looking for young people with a diagnosis of DCD/dyspraxia
between the age of 12 and 16. You have been invited to take part because you might be
suitable. Your parent/guardian has also agreed for you to take part.
Do I have to take part?
Remember, being in this study is up to you. Even if your parents give their permission
for you to participate in this study, you still can decide for yourself if you want to take
part. You don’t have to be in this study if you don’t want to! Even if you agree to take
part in the study, you can still stop at any time without giving a reason. If you decide
not to take part, this will not affect you negatively in any way.
What will happen if I take part?
If you agree to be in this study, we will ask you to sign a consent form. We will then ask
you to complete a questionnaire which asks you about your mood and emotions. It should
take approximately 10 minutes and can be completed online, over the phone, or on paper.
83
Unfortunately, you will not receive any money or reward for taking part. Your
parent/guardian will be given the option at the end of the survey to enter a prize draw
for a £100 Amazon voucher. The winner will be contacted by email at the end of study
in April 2018.
Will information about me be available to anyone?
The information that we collect from you is confidential and anonymous. Only members
of our team will be able to see this information. Your school and your parents/guardians
will not have access to the information we collect. In our findings we will discuss the
results of many young people - we do not single out or name any one participant.
The only other time that we will tell somebody else about something you have said is if
we think you or someone else may be at risk of harm.
This research study has been reviewed and given a Favourable Ethical Opinion by Faculty
of Health and Medical Sciences Ethics Committee, at the University of Surrey. This
means that the study has been checked and it is ethical for it to be conducted.
What if I have a question or there is a problem?
You can ask any questions that you have about the study at any time. If you have a
question you can contact me or other people in my team using the contact details below.
Serif Omer Dr Hayley Leonard
Trainee Clinical Psychologist Lecturer
School of Psychology School of Psychology
AD Building AD Building
University of Surrey University of Surrey
Guildford Guildford
GU2 7XH GU2 7XH
[email protected] [email protected]
01483 686888
Thank you for taking the time to read this Information Sheet.
84
Parent Information Sheet (TD group; 07.11.17; Version 2) Title of Project Executive function and internalizing problems in adolescents with and without Developmental Coordination Disorder Introduction We would like to invite you and your child to take part in a research project. Before you and your child decide to take part, you need to understand why the research is being done and what it will involve. Please take the time to read the following information carefully. Talk to others about the study if you wish. This study is being conducted by Serif Omer (Trainee Clinical Psychologist), under the supervision of Dr Hayley Leonard (Lecturer in Developmental Psychology and Neurodevelopmental Disorders). Please ask questions if there is anything you do not understand. What is the purpose of the study? We know that adolescents with Developmental Coordination Disorder (DCD; sometimes also called ‘Dyspraxia’) often have difficulties with high-level thinking abilities, such as planning and memory. They also often report increased symptoms of anxiety and depression compared to others their age without the disorder. The current project aims to investigate this further by understanding how these difficulties may be related to each other. To understand this, we need to also recruit adolescents without dyspraxia, which is why we are inviting your child to participate in the study. Why have I been invited to take part in the study?
As part of this study, we are seeking to recruit adolescents without a diagnosis of DCD / dyspraxia between the age of 12 and 16 and one of their parents/guardians. You and your child have been invited to take part because you might meet these criteria. Do I have to take part? No, neither you nor your child has to participate. There will be no adverse consequences if you decide not to participate. You can also withdraw your participation at any time without giving a reason.
85
What will my involvement require?
As the child’s parent or guardian, you will be asked to complete a consent form and some initial information about your child (e.g. date of birth). You will then be asked a set of questions which can be completed on paper or, if preferred, online or over the phone. This should take no more than 30 minutes in total and will include questions about your child’s movement abilities (such as sports skills, handwriting, etc.) and their high-level thinking skills (such as planning and memory). You will not receive any payment for taking part. You will be given the option at the end of the survey to enter a prize draw for a £100 Amazon voucher. The winner will be contacted by email at the end of study in April 2018. What will my child’s involvement require?
If you consent for your child to take part and they are suitable for the study, they will be asked to complete a questionnaire concerning their moods and emotions. In total this should take no more than 10 minutes. They can complete this questionnaire online, over the phone, or on paper. Your child will not receive any payment for taking part. What will I have to do?
If you and your child would like to take part, please complete the enclosed consent form and questionnaires. Please feel free to contact the research team if you have any questions. What are the possible disadvantages or risks of taking part? There is a possibility that some of the questions may highlight sensitive issues for you or your child. If you want to talk about the questions or your answers, please contact the research team. If your child appears to experience any distress, the session will be terminated immediately and the research team will alert you and/or their teachers. What are the possible benefits of taking part? It is unlikely that you or your child will benefit directly from taking part. However, it is hoped that the study will improve our understanding of people with DCD/dyspraxia, which could have clinical implications for improving the lives of this group of people. Understanding the moods and emotions of adolescents without DCD/dyspraxia, and how they affect skills that are central to learning such as planning and memory, will also be of great use to teachers and researchers.
86
What happens when the research study stops?
You may receive a summary of the research findings at the end of the study (after February 2018). You can indicate if and how you would like to receive this on the initial screening questionnaire. This summary will only include the overall findings of the study. We will not provide individual feedback on your child’s or your own responses. What if there is a problem?
Any complaint or concern about any aspect of the way you have been dealt with during the course of the study will be addressed; please contact Dr Hayley Leonard (Research Supervisor) on 01483 686888 or [email protected]. You may also contact the Head of School, Professor Derek Moore, on 01483 686933 or [email protected]. Will taking part in the study be kept confidential? Yes. All of the information that you and your child give will be anonymised so that those reading reports from the research will not know who has contributed to it. All project data will be held for at least 6 years and all research data for at least 10 years in accordance with University policy. Data will be stored securely in accordance with the Data Protection Act 1998. However, should you or your child disclose information that suggests your child is at risk then the researcher may need to report this to an appropriate authority. This would usually be discussed with you first. Contact details
Serif Omer Trainee Clinical Psychologist [email protected] Dr Hayley Leonard Lecturer [email protected] School of Psychology AD Building University of Surrey Guildford GU2 7XH 01483 686888
87
Who is organising and funding the research?
This research is unfunded and is being completed by Serif Omer as part of a Doctorate in Clinical Psychology at the University of Surrey. Who has reviewed the project? The study has been reviewed and received a Favourable Ethical Opinion (FEO) from the Faculty of Health and Medical Sciences Ethics Committee, at the University of Surrey. Thank you for taking the time to read this Information Sheet.
88
Adolescent Information Sheet (TD group; 07.11.17; Version 2)
Title of Project
Executive function and internalizing problems in adolescents with and without
Developmental Coordination Disorder
Introduction
Hi, my name is Serif Omer and I would like to invite you to take part in a research
study. At the University of Surrey, we are trying to learn more about the effect of
movement skills on young people’s mood and thinking. We are comparing young people
with no movement difficulties, like you, with young people who do have movement
difficulties.
Why is this study being done?
People with Developmental Coordination Disorder (DCD), which is sometimes called
‘Dyspraxia’, have difficulties with movement tasks (such as handwriting and sports).
However, they may also have difficulties with their mood and some thinking skills (such
as memory and planning ahead). We would like to know more about whether young
people with DCD have differences in their mood and thinking skills compared to young
people without DCD and why this might be. We hope that this research will help to
better understand the effect of DCD on young people which could help to improve
their lives. This research could also help to better understand difficulties with mood
and thinking skills in young people, like you, that do not have DCD.
Why have I been invited to take part?
As part of this study, we are looking for young people between the age of 12 and 16
who do not have DCD/dyspraxia. You have been invited to take part because you might
be suitable. Your parent/guardian has also agreed for you to take part.
Do I have to take part?
Remember, being in this study is up to you. Even if your parents give their permission
for you to participate in this study, you still can decide for yourself if you want to
take part. You don’t have to be in this study if you don’t want to! Even if you agree to
take part in the study, you can still stop at any time without giving a reason. If you
decide not to take part, this will not affect you negatively in any way.
What will happen if I take part?
If you agree to be in this study, I will ask you to sign a consent form. I will also ask you
to complete a questionnaire which asks you about your mood and emotions.
Unfortunately, you will not receive any money for taking part. Your parent/guardian
will be given the option at the end of the survey to enter a prize draw for a £100
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Amazon voucher. The winner will be contacted by email at the end of study in April
2018.
Will information about me be available to anyone?
The information that we collect from you is confidential and anonymous. Only members
of our team will be able to see this information. Your school and your
parents/guardians will not have access to the information we collect. In our findings
we will discuss the results of many young people - we do not single out or name any one
participant.
However, if your parent/guardian has a concern, we may share a report of your
strengths and weaknesses with them which they can pass on to a professional if they
so choose. The only other time that we will tell somebody else about something you
have said is if we think you or someone else may be at risk of harm.
This research study has been reviewed and given a Favourable Ethical Opinion by
Faculty of Health and Medical Sciences Ethics Committee, at the University of Surrey.
This means that the study has been checked and it is ethical for it to be conducted.
What if I have a question or there is a problem?
You can ask any questions that you have about the study at any time. If you have a
question you can contact me or other people in my team using the contact details
below.
Serif Omer
Trainee Clinical Psychologist
Dr Hayley Leonard
Lecturer
School of Psychology
AD Building
University of Surrey
Guildford
GU2 7XH
01483 686888
Thank you for taking the time to read this Information Sheet.
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Appendix G: Parent consent form
A copy of the parent consent form is provided on the following page.
91
Parent Consent Form [version 1, date 26.09.2016] Executive function and internalizing problems in adolescents with and without Developmental Coordination Disorder Please initial each box
I have read and understood the Information Sheet provided (version 2, date xx/xx/xx). I have been given a full explanation by the investigators of the nature, purpose, location and likely duration of the study, and of what my child and I will be expected to do.
I have been advised about the potential for some questions to be of a sensitive nature for my child and/or myself. I have been given the opportunity to ask questions on all aspects of the study and have understood the advice and information given as a result.
I agree to comply with the requirements of the study as outlined to me to the best of my abilities. I shall inform the investigators immediately if I have any concerns.
I agree for my child’s and my own anonymised data to be used for this study that will have received all relevant ethical approvals.
I understand that all project data will be held for at least 6 years and all research data for at least 10 years in accordance with University policy and that my personal data is held and processed in the strictest confidence, and in accordance with the UK Data Protection Act (1998).
I understand that my child and I are free to withdraw from the study at any time without needing to justify our decision, without prejudice and without our legal rights and school education being affected.
I understand that I can request for my data and my child’s data to be withdrawn until publication of the data and that following my request all personal data already collected from us can be destroyed.
Optional. I agree for the researchers to contact me to provide me with a study results summary.
Optional. I agree for the researchers to contact me about future studies.
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I confirm that I have read and understood the above and freely consent to participating in this study. I have been given adequate time to consider my participation.
Name of child: …….............................................. (BLOCK CAPITALS) Name of parent/guardian …….............................................. (BLOCK CAPITALS) Signed: …….............................................. Date: ……..............................................
Name of researcher taking consent: ……..............................................
(BLOCK CAPITALS) Signed: ……..............................................
Date: ……..............................................
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Appendix H: Adolescent assent form
A copy of the adolescent assent form is provided on the following page.
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Adolescent Assent Form [version 1, date 08.08.2016] Executive function and internalizing problems in adolescents with and without Developmental Coordination Disorder Please tick yes or no
Have you read (or been read to) about this research study? Yes No
Has somebody explained this research study to you? Yes No
Do you understand what the research study is about? Yes No
Have you asked all the questions you want? Yes No
Have you had your questions answered in a way you Yes No understand?
Do you understand it’s okay to say you don’t want to Yes No take part?
Do you understand it’s okay to stop taking part at any time? Yes No
Are you happy to take part? Yes No
If any answers are ‘no’ or you don’t want to take part, don’t sign your name on this form. If you do want to take part, please write your name and today’s date.
Your name: …….............................................. Date: …….............................................. Name of researcher taking consent:
……..............................................
Signed: .................................................... Date: …………………………………………………
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Appendix I: Eligibility screening questionnaire
Please answer the following questions about your child:
1. Date of birth: …………………………………………………………….
2. Gender: Male Female Other
3. a. Have they received a diagnosis of Developmental Coordination Disorder
(sometimes also known as Dyspraxia); or have they been referred for an
assessment of Developmental Coordination Disorder?
Yes, diagnosed Awaiting assessment No
b. If yes, are you able to provide a diagnostic report to the research team? Yes No
4. Have they received a diagnosis of an Attention Deficit Hyperactivity Disorder
(ADHD); or have they been referred for an assessment of Attention Deficit
Hyperactivity Disorder?
Yes, diagnosed Awaiting assessment No
5. Have they received a diagnosis of an Autism Spectrum Disorder (ASD)
(sometimes also known as Asperger’s syndrome); or have they been referred
for an assessment Autism Spectrum Disorder?
Yes, diagnosed Awaiting assessment No
6. Would you like to be contacted after the study to receive a summary of the
overall findings?
Yes, by email Yes, by post No
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Appendix J: Favourable ethical opinion
Chair’s Action Proposal Ref: 1214-PSY-16
Names of Student/Trainee:
SERIF OMER
Title of Project: Executive function and internalizing problems in adolescents with and without Development Coordination Disorder
Supervisors: Dr Hayley Leonard
Date of submission: Date of resubmission:
16th August, 2016 27th September 2016
The above Research Project has been re-submitted to the Faculty of Health and Medical Sciences Ethics Committee and has received a favourable ethical opinion on the basis described in the protocol and supporting documentation. The final list of documents reviewed by the Committee is as follows: Ethics Application Form Detailed protocol for the project Participant Information sheet Consent Form Risk Assessment Insurance Documentation (If appropriate)
All documentation from this project should be retained by the student/trainee in case they are notified and asked to submit their dissertation for an audit.
Signed and Dated: _27/09/2016________________
Dr Anne Arber, Professor Bertram Opitz Co-Chairs, Ethics Committee
Please note: If there are any significant changes to your proposal which require further scrutiny, please contact the Faculty of Health and Medical Sciences Ethics Committee before proceeding with your Project.
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Appendix K: Assumptions for independent samples t-tests
Data plots
Histograms, Q-Q plots, and boxplots were created for each of the study groups to
explore the data for outliers and normality.
(i) Internalising symptoms (RCADS Total):
TD group DCD group
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(ii) Executive function difficulties (BRIEF GEC):
TD group DCD group
99
Outliers
The data was explored for univariate outliers prior to further analyses. No
outliers were identified on inspection of histograms or boxplots. Z-scores were also
calculated for each variable, where 5% of the total sample (n = 2.15) were expected to
exceed +/-1.98, 1% (n = 0.43) were expected to exceed +/-2.58, and 0% expected to
exceed +/-3.29 (Field, 2013). On the RCADS Total, only one data point exceeded a Z-
score of +/-1.98 (fewer than the 5% cut-off) and no data points exceeded +/-2.58. On
the BRIEF GEC, two data points exceeded +/-1.98 (at the expected level) and no data
points exceeded +/-2.58. This suggests that no univariate outliers were present.
Normality
The data were explored for normality. Inspection of histograms and Q-Q plots
indicated that the data was skewed for both the RCADS Total and BRIEF GEC in both
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study groups. Skewness and kurtosis scores were calculated for each variable and
divided by their standard error to obtain z-scores (see Table K1). All scores were within
the cut-off for significance (1.96) suggesting the distributions did not differ significantly
from a normal distribution. Both the Kolmogorov-Smirnov test and Shapiro-Wilk test
were conducted to explore whether the sample differed significantly from a normal
distribution. These tests identified that both the RCADS Total and BRIEF GEC differed
significantly form a normal distribution in the TD group, but not in the DCD group.
Considering all this information, the data for both the RCADS Total and BRIEF GEC
were not considered to meet the assumption of normal distribution. As such,
bootstrapping was used in the analyses which is considered robust to violations of this
assumption (Field, 2013).
Table K1. Normality statistics for study variables
Variable Skewness z-
score
Kurtosis z-score Kolmogorov-
Smirnov test (p)
Shapiro-Wilk test
(p)
TD DCD TD DCD TD DCD TD DCD
RCADS-25
Total
1.53 0.040 -0.97 -1.142 .018* .200 .012* .466
BRIEF GEC 1.8 -1.382 -0.37 -0.049 .070 .140 .011* .195
*Significantly different from a normal distribution (p < .05) BRIEF GEC: Behaviour Rating Inventory of Executive Function – Global Executive Index; DCD:
Developmental Coordination Disorder; RCADS-25: Revised Child Anxiety and Depression Scale – Short
version; TD: Typically developing
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Homogeneity of variance / homoscedasticity
The variance of the outcome variable was explored for homogeneity. The
variance ratios between the two groups indicated that the variances were approximately
equal (RCADS Total: 1.38; BRIEF GEC: 1.76). In support of this, Levene’s test was not
significant for both the RCADS Total, F (1, 41) = 1.033, p = .315, and BRIEF GEC, F
(1, 41) = 1.720, p = .197). This suggests that the variance was stable at each level of the
independent variable (DCD Status).
102
Appendix L: Assumptions for simple mediation analysis
The main assumptions for linear regression were explored for each path in the mediation
analysis (i.e. path a, b and c).
Multivariate outliers / influential cases
For each regression, the standardised residuals (z-scores) were calculated. It was
expected that 2.15 cases (5% of total sample) would have standardised residuals
exceeding +/-1.96 standard deviations from the mean, 0.43 cases (1%) would exceed +/-
2.58, and zero cases (0%) would exceed +/- 3.29 (Field, 2013). Each regression was also
explored for influential cases. Cook’s distance was calculated, whereby scores greater
than 1 indicate the case is having an undue influence on the model (Cook, 1977).
Leverage values were calculated, whereby values greater than three times the average
leverage indicate undue influence (Stevens, 2002). Finally, Mahalanobis distances were
calculated, whereby values exceeding 11 were deemed as having undue influence (the
cut-off suggested for very small sample sizes with two predictors; Field, 2013).
Path a: One case (2.3%) exceeded +/-1.96 standard deviations from the mean
and zero cases exceeded +/- 2.58 standard deviations from the mean. This is within
expected levels, given the small sample size. Further examination indicated that no cases
had a Cook’s distance higher than 1 (highest value = 0.13). Zero cases had leverage
values larger than three times the average Leverage (Average Leverage = 0.05; highest
value = 0.05). No values had a Mahalanobis value greater than 11 (highest value = 2.02).
Given the above, no cases were deemed to have had any undue influence on the model.
103
Path b: One case (2.3%) exceeded +/-1.96 standard deviations from the mean
and zero cases exceeded +/- 2.58 standard deviations from the mean. This is within
expected levels, given the small sample size. Further examination indicated that no cases
had a Cook’s distance higher than 1 (highest value = 0.14). Zero cases had leverage
values larger than three times the average Leverage (Average Leverage = 0.07; highest
value = 0.18). No values had a Mahalanobis value greater than 11 (highest value = 7.43).
Given the above, no cases were deemed to have had any undue influence on the model.
Path c: Zero cases (0%) exceeded +/-1.96 standard deviations from the mean.
Further examination indicated that no cases had a Cook’s distance higher than 1 (highest
value = 0.13). Zero cases had leverage values larger than three times the average
Leverage (Average Leverage = 0.05; highest value = 0.05). No values had a
Mahalanobis value greater than 11 (highest value = 2.02). Given the above, no cases
were deemed to have had any undue influence on the model.
Independence of errors
Durbin-Watson statistics were calculated for each regression model to explore
the assumption of independent errors (i.e. the residuals within the model are
uncorrelated). This assumption was met if values were close to 2 (Durbin & Watson,
1950, 1951).
Path a: The data met the assumption of independent errors as the Durbin-
Watson statistic lay very close to 2 (Durbin-Watson = 1.904).
Path b: The data met the assumption of independent errors as the Durbin-
Watson statistic lay very close to 2 (Durbin-Watson = 1.971).
104
Path c: The data met the assumption of independent errors as the Durbin-Watson
statistic lay very close to 2 (Durbin-Watson = 1.771).
Linearity and homoscedasticity
A graph depicting the standardised residuals against the standardised predicted
values was plotted for the model including both the independent variable (IV) and
mediator (M) as predictors (i.e. path b). Data points were generally dispersed randomly
and evenly throughout the plot indicate that linearity and homoscedasticity can be
assumed. Homogeneity of variance was previously explored and assumed for paths a
and c prior to conducting t tests (see Appendix K).
105
Normally distributed errors
Histograms and P-P plots of the standardised residuals were created for each
regression model to explore the distribution of errors (see below). They show that the
distribution of errors was approximately normally distributed, at least sufficiently for
bootstrapping analyses.
Path a:
Path b:
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Path c:
Homogeneity of regression
The data were tested to check that the relationship between the mediator and
dependent variable (DV) were not dependent on the IV. When including the interaction
between DCD status and BRIEF GEC in the model, the interaction was not significant (p
= .192).
Multicollinearity
The data was assessed for multicollinearity prior to conducting the mediation
analysis. Pearson’s correlation coefficients between the key predictor variables indicated
no correlations were higher than .90. Correlations of .90 or more are suggestive of
multicollinearity (Field, 2013). Further tests also indicated that the VIF level was below
10 (Bowerman & O’Connell, 1990; Myers, 1990) and tolerance was above 0.2 (Menard,
1995) when entering both predictors (DCD status and BRIEF GEC) into the model
(VIF= 4.182; tolerance = 0.239.
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Appendix M: Assumptions for subscale analyses using independent samples t-tests
Data plots
Histograms, Q-Q plots, and boxplots were created for each subscale of the
RCADS-25 and BRIEF across each study group to explore the data for outliers and
normality.
(i) Depression symptoms (RCADS-25 Depression):
TD group DCD group
108
Anxiety symptoms (RCADS-25 Anxiety):
TD group DCD group
109
(ii) Behavioural regulation difficulties (BRIEF BRI):
TD group DCD group
110
(iii) Metacognitive difficulties (BRIEF MCI):
TD group DCD group
111
Outliers
The data was explored for univariate outliers prior to further analyses. No
significant outliers were identified on inspection of histograms or boxplots. Z-scores
were also calculated for each variable, where 5% of the total sample (n = 2.15) were
expected to exceed +/-1.98, 1% (n = 0.43) were expected to exceed +/-2.58, and 0%
expected to exceed +/-3.29 (Field, 2013). On the RCADS-25 Depression subscale, only
one data point exceeded a Z-score of +/-1.98 (fewer than the 5% cut-off) and no data
points exceeded +/-2.58. On the RCADS-25 Anxiety subscale, two data points exceeded
+/-1.98 (at the expected level) and no data points exceeded +/-2.58. Zero cases exceeded
a z-score of +/-1.96 on both the BRIEF BRI and BRIEF MCI. This suggests that no
univariate outliers were present.
Normality
The data were explored for normality. Inspection of histograms and Q-Q plots
indicated that the data was skewed for all subscales in both study groups. Skewness and
112
kurtosis scores were calculated for each variable and divided by their standard error to
obtain z-scores (see Table M1). The RCADS-25 Anxiety subscale in the TD group
exceeded the cut-off for significance (+/-1.96), indicating that it was significantly
negatively skewed. Both the Kolmogorov-Smirnov test and Shapiro-Wilk test were
conducted to explore whether the samples differ significantly from a normal distribution.
A combination of these tests indicated that all subscales differed significantly from a
normal distribution in the TD group, but not in the DCD group. Considering all this
information, the data for the subscales were not considered to meet the assumption of
normal distribution. As such, bootstrapping was used in the analyses which is considered
robust to violations of this assumption (Field, 2013).
Table M1. Normality statistics for subscale variables
Variable Skewness z-score Kurtosis z-score Kolmogorov-
Smirnov test (p)
Shapiro-Wilk
test (p)
TD DCD TD DCD TD DCD TD DCD
RCADS-25
Depression
1.94 -1.05 -0.22 -0.48 .025* .200 .021* .296
RCADS-25 Anxiety 2.47* 0.94 0.63 -0.66 .018* .184 .008* .195
BRIEF BRI 0.74 -0.76 -1.40 -0.82 .200 .200 .049* .471
BRIEF MCI 1.83 -1.21 -0.33 0.67 .170 .200 .009* .683
*Significantly different from a normal distribution (p < .05)
BRI: Behavioural Regulation Index; BRIEF: Behaviour Rating Inventory of Executive Function; DCD:
Developmental Coordination Disorder; MCI: Metacognitive Index; RCADS-25: Revised Child Anxiety
and Depression Scale – Short version; TD: Typically developing
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Homogeneity of variance / homoscedasticity
The variance of the outcome variable was explored for homogeneity. The
variance ratios between the two groups indicated that the variances were approximately
equal (RCADS-25 Depression: 1.07; RCADS-25 Anxiety: 1.40; BRIEF BRI: 1.11;
BRIEF MCI: 1.60). In support of this, Levene’s test was not significant for all outcomes,
largest: F (1, 41) = 1.38, p = .247. This suggests that the variance was stable at each
level of the independent variable (DCD Status).
114
Appendix N: Assumptions for parallel multiple mediation analysis based on
subscales
The assumptions for linear regression were explored for each path in the parallel
multiple mediation analyses (i.e. paths a1, a2, b1, b2, c). This included separate analyses
with the RCADS-25 Depression and RCADS-25 Anxiety scores as the DV.
Multivariate outliers / influential cases
For each regression, the standardised residuals (z-scored) were calculated. The
models ranged from having 0 to 1 cases exceeding +/-1.96 standard deviations from the
mean. Among all models, no cases had a Cook’s distance higher than 1 (highest values:
0.13 to 15). No cases had Leverage value greater than three times the average Leverage
(highest values: 0.05 to 0.17). No cases had a Mahalanobis value greater than 11
(highest values: 2.02 to 7.02). Given the above, no cases were deemed to have had any
undue influence on any of the models.
Independence of errors
Durbin-Watson statistics were close to 2 for all models (range: 1.693 to 2.147).
Linearity and homoscedasticity
A graph depicting the standardised residuals against the standardised predicted
values was plotted for the models including all predictors. Data points were generally
dispersed randomly and evenly throughout the plots indicating that linearity and
115
homoscedasticity can be assumed for both models. Homogeneity of variance was
previously explored and assumed for paths a and c prior to conducting t-tests (see
Appendix M).
RCADS-25 Depression RCADS-25 Anxiety
Normally distributed errors
Histograms and P-P plots of the standardised residuals were created for each
regression model. They show that the distribution of errors was approximately normally
distributed. Plots of the models including all predictors are displayed below.
RCADS-25 Depression RCADS-25 Anxiety
116
Homogeneity of regression
The data were tested to check that the relationship between the mediators and
DV’s were not dependent on the IV. When including the interaction between IV and
M’s, the interaction was not significant (range of p = .068 to .248).
Multicollinearity
The VIF level was below 10 (Bowerman & O’Connel, 1990; Myers, 1990) and
tolerance was above 0.2 (Menard, 1995) for all variables (range, VIF= 3.77-4.27;
tolerance = 0.234-2.65).
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Appendix O: Assumptions for simple mediation analysis within the TD sample
The main assumptions for linear regression were explored for each path in the
mediation analysis (i.e. path a, b and c) with the DCDQ-07 as the IV (TD group only).
Multivariate outliers / influential cases
For each regression, the standardised residuals (z-scores) were calculated. It was
expected that 1.60 cases (5% of total sample) would have standardised residuals
exceeding +/-1.96 standard deviations from the mean, 0.32 cases (1%) would exceed +/-
2.58, and zero cases (0%) would exceed +/- 3.29 (Field, 2013). Cook’s distance,
leverage values, and Mahalanobis distances were also calculated.
Path a: Two cases (6.25%) exceeded +/-1.96 standard deviations from the mean
and zero cases exceeded +/- 2.58 standard deviations from the mean. No cases had a
Cook’s distance higher than 1 (highest value = 0.12). Zero cases had leverage values
larger than three times the average Leverage (Average Leverage = 0.03; highest value =
0.09). No values had a Mahalanobis value greater than 11 (highest value = 6.07). Given
the above, no cases were deemed to have had any undue influence on the model.
Path b: One case (3.13%) exceeded +/- 2.58 standard deviations. No cases had a
Cook’s distance higher than 1 (highest value = 0.21). One case had a leverage value
larger than three times the average Leverage (Average Leverage = 0.06; highest value =
0.22). No values had a Mahalanobis value greater than 11 (highest value = 6.71). Given
the above, no cases were deemed to have had any undue influence on the model.
118
Path c: One case (3.13%) exceeded +/-1.96 standard deviations from the mean
and no cases exceeded +/-2.58 standard deviations. Further examination indicated that
no cases had a Cook’s distance higher than 1 (highest value = 0.14). Two cases had
leverage values larger than three times the average Leverage (Average Leverage = 0.03;
highest value = 0.19). No values had a Mahalanobis value greater than 11 (highest value
= 6.07). Given the above, no cases were deemed to have had any undue influence on the
model.
Independence of errors
The data met the assumption of independent errors as the Durbin-Watson statistic
lay very close to 2 (Durbin-Watson range = 1.792-2.14).
Linearity and homoscedasticity
A graph depicting the standardised residuals against the standardised predicted
values was plotted for each path. Data points were dispersed randomly and
approximately evenly throughout the plot indicating that linearity and homoscedasticity
can be assumed.
119
Path a:
Path b:
Path c:
120
Normally distributed errors
Histograms and P-P plots of the standardised residuals were created for each
regression model to explore the distribution of errors (see below). They show that the
distribution of errors was approximately normally distributed, at least sufficiently for
bootstrapping analyses.
Path a:
Path b:
121
Path c:
Multicollinearity
The data was assessed for multicollinearity prior to conducting the mediation
analysis. Pearson’s correlation coefficients between the key predictor variables indicated
no correlations were higher than .65. Further tests also indicated that the VIF level was
below 10 (Bowerman & O’Connell, 1990; Myers, 1990) and tolerance was above 0.2
(Menard, 1995) when entering both predictors (DCDQ-07 and BRIEF GEC) into the
model (VIF= 1.00; tolerance = 1.00).
122
Part 2: Major Research Project Literature review
Internalising symptoms in Developmental Coordination Disorder: A
systematic review and meta-analysis
Word count: 6175
Statement of Journal Choice
The Journal of Child Psychology and Psychiatry
‘The Journal of Child Psychology and Psychiatry’ publishes research that advances the
understanding of developmental psychopathology and that informs theory and clinical
practice. It is a leading journal for child and adolescent psychology and psychiatry. The
journal has confirmed interest in this paper for submission to their ‘Research Reviews’
section. See Appendix for more details.
123
Abstract
Background: Developmental Coordination Disorder (DCD) affects 5-6% of children.
There is growing evidence that DCD is associated with greater levels of internalising
symptoms (i.e. depression and anxiety). This is the first systematic review and meta-
analysis to explore the magnitude of this effect, the quality of the evidence, and potential
moderators. Methods: A systematic search was conducted to identify studies reporting a
comparison between individuals with DCD/probable DCD and typically developing
(TD) individuals on measures of internalising symptoms. A pooled effect size (Hedges
g) was calculated using random effects meta-analysis. Study quality, publication bias
and potential moderators of the effect were explored. Results: Twenty studies, including
a total of 23 subsamples, met the inclusion criteria, of which 22 subsamples were
included in the meta-analysis (DCD: n = 1123; TD: n = 7346). A significant, moderate
effect of DCD on internalising symptoms was found (g = 0.61). This effect remained
robust after accounting for publication bias and excluding lower quality studies. The
effect was significantly larger in studies utilizing a cross-sectional design (vs.
longitudinal), convenience sampling (vs. population screening) and a majority male
sample. Conclusions: The findings demonstrate that individuals with DCD experience
greater levels of internalising symptoms than their peers. This highlights the importance
of routine screening for emotional difficulties in DCD, raising awareness of the
condition in mental health services, and developing psychosocial interventions that
extend beyond a focus on motor impairments. However, there is a need for higher
quality, longitudinal studies to better understand the causal relationship between DCD
and internalising symptoms.
124
Keywords: Developmental Coordination Disorder, DCD, Internalising
symptoms, depression, anxiety, mental health, meta-analysis.
125
Introduction
Developmental Coordination Disorder (DCD) is a neurodevelopmental disorder
affecting between 5-6% of children and is characterised by significant impairment to an
individual’s ability to perform everyday motor tasks (American Psychiatric Association
[APA], 2013). This can include difficulties with self-care (e.g. tying shoelaces, brushing
teeth), academic tasks (e.g. handwriting), and leisure activities (e.g. catching a ball,
balancing). A diagnosis of DCD is based on four criteria (APA, 2013): (a) performance
in motor coordination tasks is substantially below expectation given the person’s age
and opportunities; (b) the motor coordination difficulties significantly interfere with
activities of daily living or academic achievement; (c) difficulties began in the early
developmental period; and (d) the difficulties cannot be attributed to an intellectual
disability or neurological condition (e.g. cerebral palsy). DCD is sometimes referred to
as ‘dyspraxia’. However, there is no internationally agreed definition for the term
dyspraxia, it is not included in diagnostic manuals and it is sometimes used to refer to a
broader range of difficulties beyond those characterising DCD. As such, the term DCD
is used hereafter.
Despite its prevalence, DCD often goes unrecognised and is poorly understood
among healthcare and education professionals (Gaines, Missiuna, Egan, & McLean,
2008; B. N. Wilson, Neil, Kamps, & Babcock, 2013). This is of concern given that DCD
has been found to have a significant impact not just on an individual’s motor abilities,
but across a wide range of psychological, cognitive, physical and social domains
(Zwicker, Harris, & Klassen, 2013). For example, children with DCD have been found
to engage in less physical activity (Cairney, Hay, Veldhuizen, Missiuna, & Faught,
126
2010), to be at an increased risk of obesity (Cairney & Veldhuizen, 2013), to
underachieve in academic performance (Gomez et al., 2015), to be more socially
isolated (Chen & Cohn, 2003) and to have lower self-esteem (Miyahara & Piek, 2006)
compared to their typically developing (TD) peers. There is also evidence that the
impact of DCD across these domains persists through childhood and into adulthood
(Cousins & Smyth, 2003; Hill, Brown, & Sorgardt, 2011; Kirby, Sugden, Beveridge, &
Edwards, 2008). DCD also often co-occurs with other developmental disorders,
including Attention Deficit Hyperactivity Disorder (ADHD) and Autism Spectrum
Disorder (ASD; Pieters, et al. 2012).
One area that has received increasing attention is the impact of DCD on mental
health, specifically internalising symptoms. ‘Internalising’ is a broad construct referring
to symptoms of both depression and anxiety, which have been found to commonly
overlap in childhood and adolescence (Eaton et al., 2013; Kovacs & Devlin, 1998).
There is growing evidence that individuals with DCD have elevated levels of
internalising symptoms compared to their TD peers (Mancini, Rigoli, Cairney, Roberts,
& Piek, 2016). Research has also found associations between motor abilities and
internalising symptoms in community samples of TD children and adults (Poole et al.,
2016; Rigoli, Piek, & Kane, 2012; A. Wilson, Piek, & Kane, 2013), an increased risk of
psychiatric disorders in individuals with DCD (Rasmussen & Gillberg, 2000), and
impaired motor abilities in individuals with common psychiatric disorders (Damme,
Simons, Sabbe, & van West, 2015). The Environmental Stress Hypothesis is a
framework that was introduced to account for this relationship between DCD and mental
health (Cairney, Rigoli, & Piek, 2013). It suggests that the motor impairments in DCD
127
can expose an individual to a variety of secondary psychosocial stressors which over
time can lead to poorer mental health (see Figure 1). These proposed mediators include
physical (e.g. physical inactivity), social (e.g. interpersonal conflict, reduced social
resources), and personal factors (e.g. reduced self-esteem).
Figure 1. Diagram depicting the Environmental Stress Hypothesis as an explanation for
internalising symptoms in DCD (from Mancini et al. 2016).
Understanding the link between DCD and mental health has important
implications for assessment and intervention with this population, including at schools,
physical health services and mental health services. To date, several reviews have
summarised the findings on internalising symptoms in DCD (Caçola, 2016; Mancini et
al., 2016; Missiuna & Campbell, 2014). However, they consist of narrative summaries
only. There are also inconsistent findings, with some studies finding no significant effect
128
(Davis, Ford, Anderson, & Doyle, 2007; King-Dowling, Missiuna, Rodriguez,
Greenway, & Cairney, 2015) and others a large effect (Dewey, Kaplan, Crawford, &
Wilson, 2002; Pratt & Hill, 2011). A systematic search, synthesis and critical appraisal
of the evidence can provide a more rigorous understanding of this relationship. A meta-
analysis to pool the findings would provide a more accurate understanding of whether
individuals with DCD do indeed experience greater internalising symptoms than their
peers and would provide insight into the magnitude of this difference.
Studies also vary greatly in their design, participants, measures, and
methodological quality. Whereas some studies have recruited participants with a
confirmed diagnosis of DCD, others have included only those identified as ‘probable
DCD’ based on screening measures. Studies also differ in how well they controlled for
confounding variables, whether they employed a longitudinal or cross-sectional design,
and whether they recruited participants through population-based screening or
convenience sampling. There is also some evidence to suggest the impact may be greater
in adolescents compared to younger children (Piek et al., 2007; Skinner & Piek, 2001),
in males compared to females (Sigurdsson et al., 2002), and in individuals with
comorbid ADHD (Missiuna et al., 2014; Piek et al., 2007). A meta-analytic approach
allows for an investigation into the potential sources of heterogeneity across studies,
which could help to guide future research and intervention.
The aim of this paper was, therefore, to conduct a systematic review and meta-
analysis of studies that compared individuals with DCD to TD individuals on measures
of internalising symptoms; to appraise the quality of the evidence; and to explore which
factors moderate the effect. The focus was on severity levels of internalising symptoms,
129
as opposed to rates of actual diagnosis, given that most studies have adopted severity
outcome measures, and given that data on diagnostic rates may obscure important
differences in actual symptoms.
Method
The review was protocol-driven and carried out in accordance with
recommended guidelines for systematic reviews (Moher, Liberati, Tetzlaff, Altman, &
The Prisma Group, 2009) and meta-analyses of observational studies (Stroup et al.,
2000).
Eligibility criteria
In line with recommended guidelines, broad inclusion criteria were used with the
aim to later explore the impact of specific design features. Articles were eligible if they:
(a) included participants, of any age, with a confirmed diagnosis of DCD according to
DSM-IV or DSM-5 criteria; or who were identified as having motor coordination
difficulties consistent with DCD (i.e. ‘probable DCD’); (b) included a comparison group
of TD individuals, as defined by the absence of diagnosed or suspected developmental
disorders; (c) measured levels of internalising symptoms (i.e. depression and/or anxiety)
for each group using self-report, parent-report, teacher-report, direct observation or
clinical interview; (d) reported statistics that could be transformed into a standardised
mean difference (e.g. mean and standard deviations); and (e) were available in full text
in English. Studies involving participants with a comorbid diagnosis (e.g. ADHD) were
also eligible if the motor coordination difficulties were clearly described and used as the
130
basis for group comparison (as the first criterion above). Studies were excluded if
participants’ motor difficulties were attributed to another developmental difficulty or
medical diagnosis (e.g. cerebral palsy). For studies using the label ‘dyspraxia’, they were
required to refer to overall motor impairment and not just oro-motor difficulties and
gesture. Studies were also excluded if the outcome only included rates of psychiatric
diagnoses (i.e. they did not report on a measure of the severity of internalising
symptoms).
If separate studies included overlapping samples, priority was given to the study
with the best control of important confounders (i.e. age and gender) or the study that
allowed for the most detailed exploration of moderating factors (e.g. outcomes reported
separately by gender or age group). Where the same participants were included but
different subtests reported, data were combined (Borenstein, Hedges, Higgins, &
Rothstein, 2009).
Search strategy
Studies were identified through a systematic search of Medline, PsychInfo,
CINAHL, ERIC, and Web of Science. To minimise the impact of publication bias,
unpublished studies were also searched using ProQuest Dissertations and Theses and
Open Grey. The latest search was completed on 3rd March 2018.
The search included terms related to DCD (developmental coordination disorder,
DCD, dyspraxi*, motor skills disorder, coordination difficult*, coordination problem*,
clumsy, clumsiness, motor proficiency, motor competence, motor difficult*, motor
impairment, motor dysfunction, perceptual motor difficult*, perceptual motor
131
impairment, motor skills disorder, motor learning difficult*, motor learning problem*,
motor problem*, movement disorder, psychomotor disorder) combined with terms
related to internalising symptoms (internali*, anxi*, depress*, mood, mental health,
mental illness, mental disorder, emotional problem*, psychopatholog*). Titles and
abstracts were screened by one reviewer (SO), with 25% cross-checked by a second
(AMN; percent agreement = 97.5%, Cohen’s kappa = 0.65). The full texts of all
potentially relevant articles were then screened independently by two reviewers (SO &
AMN), with disagreement resolved by consensus and discussion with a third (HL;
percent agreement = 94.5%, kappa = 0.87). The bibliographies of the included studies
and relevant review articles were screened and their citations tracked to identify
additional studies. The first authors of the included articles were also contacted to
identify any further eligible studies or to clarify missing information.
Data extraction
Data on each study were extracted into an electronic pro forma. Two researchers
(SO & AMN) performed data extraction for all included studies and inconsistencies
were discussed until consensus was reached. Interrater reliability was good for both
categorical (percent agreement = 91-100%; kappa = 0.82-1.00) and continuous
(intraclass correlation coefficient = 1.00) data.
The following information was extracted for each study: author, publication year,
country, design (cross-sectional; longitudinal), population, sampling procedure
(population-based screening; selective/convenience sample), criteria for DCD
(confirmed DCD; probable DCD), criteria for TD, number of participants, gender
132
(percentage male), age (mean and range), comorbid ADHD diagnosis (ADHD assessed
and excluded from the sample; ADHD assessed and included; ADHD not assessed),
measure of internalising symptoms, internalising construct (depression; anxiety; overall
internalising), reporter (self-report; parent-report; teacher-report; clinician/researcher-
report), and scores (means and standard deviations, other relevant statistics).
If multiple informants or measures were used to assess internalising symptoms,
they were extracted separately so that they could be pooled (see Statistical Analysis).
Preference was given to data adjusted for important confounders (e.g. gender, age) if not
matched by design. However, where studies also adjusted for additional variables (e.g.
intelligence), the unadjusted scores were preferred to ensure comparability across studies
(Voils, Crandell, Chang, Leeman, & Sandelowski, 2011). Where findings were reported
separately for subgroups (e.g. gender, age groups) these data were extracted separately
as subsamples to facilitate the moderation analysis. Where separate groups were
included for confirmed and probable DCD, only the confirmed DCD group was
extracted. Where separate groups were included for comorbid DCD/ADHD and DCD
only, the DCD only group was extracted. This allowed for a better understanding of the
specific effect of DCD on internalising problems.
Study quality
An adapted version of the Newcastle-Ottawa Scale (NOS) was used to assess
study quality (Wells et al., 2011). Each study was rated on representativeness of the
DCD group (i.e. population screening), selection of the control group (i.e. same
population as DCD), ascertainment of DCD diagnosis (i.e. confirmed DCD); control for
133
baseline internalising (for longitudinal studies), comparability of groups (i.e. control for
confounders), measurement of internalising symptoms (i.e. validated measures), length
of follow-up (i.e. at least one year follow-up), and completeness of follow-up (i.e. ≥80%
follow-up rate or <80% but unlikely to introduce bias).
For the DCD criteria to be rated as ‘confirmed DCD’, the study must have
assessed motor skills as being below the 15th percentile using performance-based
measures (Criterion A; Blank, Smits-Engelsman, Polatajko, & Wilson, 2012), as having
a significant impact on activities of daily living or academic achievement (e.g.
questionnaires or interview; Criterion B), and ruled out intellectual disability and other
neurological conditions (e.g. by interview, performance measures, medical reports;
Criterion D). Alternatively, they could have cross-checked medical records for
diagnosis. Given that many studies were published prior to publication of the DSM-5
and the introduction of Criterion C, it was not essential that studies established whether
difficulties began in the early developmental period. The confounders considered most
important for comparability of study groups were age and gender (Twenge & Nolen-
Hoeksema, 2002). The NOS satisfies relevant guidelines for quality assessment of non-
randomised studies (Sanderson, Tatt, & Higgins, 2007) and is recommended for
systematic reviews of observational studies (Deeks et al., 2003).
Statistical Analysis
The main analysis was performed using Review Manager 5 software.
Summary effect: The standardised mean difference (SMD; Hedges g) between
the DCD group and the TD group and its 95% confidence interval were calculated for
134
each study (or subsample) separately. SMD’s around 0.2 can be considered small, 0.5
moderate, and 0.8 large. Where studies reported data on multiple measures of
internalising, a pooled effect size and variance was calculated (assuming a correlation
between measures of 1, which provides a conservative estimate of the variance;
Borenstein, Hedges, Higgins, & Rothstein, 2009). Effect sizes were weighted according
to the inverse of their variance to ensure that more precise estimates influence overall
effect size most heavily and to reduce the effect of the upwardly biased estimates of
smaller studies (Hedges & Olkin, 1985). Random-effects meta-analysis was used to
calculate a summary effect for total internalising symptoms across all studies and its
95% confidence interval.
Heterogeneity: Q-statistics were used to assess for heterogeneity and the I2
statistic to quantify the proportion of the variance due to heterogeneity. Moderators were
explored to identify potential sources of heterogeneity. The following moderators were
explored: year of publication (pre-2010 vs. post-2010), design (longitudinal vs. cross-
sectional), gender (>50% male vs. ≤50% male in the DCD group), age (included
adolescents ≥12 vs. no adolescents), comorbid ADHD (assessed and excluded vs. not
assessed, or assessed but included), sampling strategy (population screen versus
selective/convenience); selection of DCD group (confirmed vs. probable DCD),
controlled for confounders (age and gender controlled vs. uncontrolled), reporter (self-
report versus informant-report), and type of internalising (overall internalising vs.
depression vs. anxiety). The significance of moderators was tested using Q-statistics.
Publication bias: Publication bias was assessed visually using a funnel plot,
where an asymmetrical distribution indicates the presence of publication bias. Egger’s
135
test was used to statistically check for publication bias (Egger, Smith, Schneider, &
Minder, 1997). Duval and Tweedie’s trim-and-fill procedure was used to compute an
adjusted effect size by imputing the effect of smaller, unpublished studies (Duval &
Tweedie, 2000). Finally, Rosenthal's (1979) Fail-safe N was calculated to determine the
number of studies with an average effect size of 0 that would have to be included to
produce a non-significant result. This number should exceed 5k + 10 (where k is the
number of studies).
Sensitivity analysis: A sensitivity analysis was conducted to calculate a pooled
effect size excluding lower quality studies (i.e. those not meeting at least five criteria on
the NOS).
Results
Search results
The search identified a total of 20 studies meeting the inclusion criteria,
consisting of 23 eligible subsamples (two studies reported outcomes separately for males
and females, one study reported separate outcomes for children and adolescents;
hereafter these are treated as separate studies). The search process is summarised in
Figure 2.
It should be noted that two articles reported outcomes at multiple time points for
the same longitudinal study (Harrowell, Hollén, Lingam, & Emond, 2017; Lingam et al.,
2012). The data from the latter time point was used (Harrowell et al., 2017) because
separate outcomes were reported for males and females, allowing for better exploration
of moderators. Two articles reported data on the same cross-sectional study (Pearsall-
136
Figure 2. PRISMA flow diagram summarising the search process.
Records identified through
database searching
(n = 4697)
Additional records identified through other sources
Grey literature (n = 160)
Bibliographies (n = 7)
Records after duplicates removed
(n = 3081)
Records screened by titles
and abstracts
(n = 3081)
Articles excluded after title and abstract screening
(n = 3008)
Full-text articles assessed for
eligibility
(n = 73)
Articles excluded after full-text screen, with reasons (n = 53)
Review / commentary (n = 14) No DCD group / based on community sample (n = 15)
No TD group / used reference group only (n = 4)
Book chapter (n = 3)
Single item outcome (n = 3)
No measure of internalising symptoms (n = 6)
Investigated motor ability in psychiatric disorders (n = 3)
Additional articles on included studies (n =2)
Outcome based on diagnosis rates, not severity (n = 1)
Met eligibility criteria, but extreme data values reported
(n= 1)
No English full text (n = 1) Articles included in
qualitative synthesis
(n = 20)
Samples included (n = 23)
Articles included in meta-
analysis (n = 19)
Samples included (n = 22)
Articles excluded from meta-analysis
(n = 1)
Based on an adult sample (n = 1)
137
Jones, Piek, Rigoli, Martin, & Levy, 2011; Piek et al., 2007), so the larger sample was
included (Piek et al., 2007). One eligible study reported extreme values for the outcome,
raising concerns around its accuracy, and was subsequently excluded (Tseng, Howe,
Chuang, & Hsieh, 2007).
Characteristics of the included studies
The characteristics of the included studies are summarised in Table 1. A total of
8469 participants were included (1123 DCD, 7346 TD). The studies were published
between 1994 and 2018. Most were from developed countries, with one study from
Taiwan. Three prospective cohort studies were identified that screened for DCD in a
cohort and assessed their internalising symptoms at a later follow-up (Harrowell et al.,
2017, male & female samples; Wagner, Jekauc, Worth, & Woll, 2016). The remaining
20 studies adopted a cross-sectional design.
Sixteen studies identified individuals with and without DCD/probable DCD via
population-based screening of community samples (Campbell, Missiuna, &
Vaillancourt, 2012; Chen, Tseng, Hu, & Cermak, 2009; Dewey et al., 2002; Francis &
Piek, 2003; Harrowell et al., 2017; King-Dowling et al., 2015; Li et al., 2018; Missiuna
et al., 2014; Piek, Bradbury, Elsley, & Tate, 2008; Schoemaker & Kalverboer, 1994;
Skinner & Piek, 2001; van den Heuvel, Jansen, Reijneveld, Flapper, & Smits-
Engelsman, 2016; Wagner et al., 2016). Of the remaining studies, five recruited DCD
participants through selective or convenience samples such as clinical referrals or
138
support groups (Crane, Sumner, & Hill, 2017; Hill & Brown, 2013; Pratt & Hill, 2011;
Wagner, Bös, Jascenoka, Jekauc, & Petermann, 2012; Watson & Knott, 2006), one
recruited participants through screening a clinical population of children born with
extremely low birth weight (Davis et al., 2007), and one sampled from a monozygotic
twin population (Piek et al., 2007).
The studies varied in their operationalisation of the DCD group. Ten studies
confirmed a DCD diagnosis via independent assessment of diagnostic criteria (Chen et
al., 2009; Harrowell et al., 2017; Missiuna et al., 2014; van den Heuvel et al., 2016;
Wagner et al., 2012) or via clinical reports (Crane et al., 2017; Hill & Brown, 2013; Pratt
& Hill, 2011; Watson & Knott, 2006). Thirteen studies identified those as probable DCD
based on performance-based tests of motor function (Davis et al., 2007; Dewey et al.,
2002; Francis & Piek, 2003; King-Dowling et al., 2015; Li et al., 2018; Piek et al., 2008;
Schoemaker & Kalverboer, 1994; Skinner & Piek, 2001; Wagner et al., 2016) or by
parent-report questionnaires (Campbell et al., 2012; Piek et al., 2007).
Most studies recruited children and adolescents, with only one study conducted
with adults (Hill & Brown, 2013). Of the child and adolescent studies, ten included
adolescents aged 12 or over (Dewey et al., 2002; Harrowell et al., 2017; Li et al., 2018;
Missiuna et al., 2014; Piek et al., 2007; Pratt & Hill, 2011; Skinner & Piek, 2001,
adolescent sample; Wagner et al., 2016; Watson & Knott, 2006). There was a mix of
male and female participants across the studies, with fourteen having majority male
participants (Campbell et al., 2012, male sample; Crane et al., 2017; Davis et al., 2007;
Dewey et al., 2002; Francis & Piek, 2003; Harrowell et al., 2017, male sample; King-
139
Table 1. Summary of characteristics of the included studies
Study Year Population DCD
assessment
DCD
sample, n
TD sample,
n
DCD age,
mean (range)
TD age,
mean (range)
DCD
gender,
% male
TD
gender,
% male
Excluded
ADHD?
(measure)
Confounders
controlled
Internalising measures,
(type)
Longitudinal studies
Harrowell et
al. (male
sample)
2017 Population screening: Birth
cohort in south-west
England, motor skills
assessed age 7.
Confirmed
DCD
(researcher
assessment)
SDQ: 109;
SMFQ: NR
(total sample
for SMFQ:
1374)
SDQ: 1780;
SMFQ: NR
(total sample
for SMFQ:
1374)
NR
(SMFQ
collected at
17.5 years;
SDQ at 16.5
years)
NR
(SMFQ
collected at
17.5 years;
SDQ at 16.5
years)
100% 100% No
(measured,
but not
excluded)
Age, gender.a
SMFQ (self-rated
depression); SDQ -
emotional subscale (self-
rated internalising)
Harrowell et
al. (female
sample)
2017 Population screening: Birth
cohort in south-west
England, motor skills
assessed age 7.
Confirmed
DCD
(researcher
assessment)
SDQ: 59
SMFQ: NR
(total sample
for SMFQ:
1803)
SDQ: 1970
SMFQ: NR
(total sample
for SMFQ:
1803)
NR
SMFQ
collected at
17.5 years;
SDQ at 16.5
years
NR
SMFQ
collected at
17.5 years;
SDQ at 16.5
years
0% 0% No
(measured,
but not
excluded)
Age, gender.a SMFQ (self-rated
depression); SDQ -
emotional subscale (self-
rated internalising)
Wagner et
al.
2016 Population screening:
Cohort of 6-10 year olds
across Germany. Motor
skills assessed age 6-10.
Probable DCD
(performance-
based test)
114 823 14.35 (12-16) 14.38 (12-16)
47.8% 49.3% No
(assessed,
not
excluded)
Gender, age,
baseline
internalising
symptoms
SDQ (parent-rated
internalising)
140
Cross-sectional Studies
Campbell et
al. (male
sample)
2012 Population screening: Fifth
grade students from
previous longitudinal study
in Ontario, Canada.
Probable DCD
(screening
questionnaire)
77 77 10.9 (10-11)b 10.9 (10-11)b 100% 100% No (not
assessed)
Age, gender BASC-2 – depression
subscale (self-rated
depression)
Campbell et
al. (female
sample)
2012 Population screening: Fifth
grade students from
previous longitudinal study
in Ontario, Canada.
Probable DCD
(screening
questionnaire)
82 82 10.9 (10-11)b 10.9 (10-11)b 0% 0% No (not
assessed)
Age, gender BASC-2 – depression
subscale (self-rated
depression)
Chen et al. 2009 Population screening: 1st-3rd
grade children in greater
Taipei area, Taiwan.
Confirmed
DCD
(researcher
assessment)
61 209 7.93 (NR)
(range for
total sample:
6.25-10.08
7.68 (NR)
(range for
total sample:
6.25-10.08
59.0% 59.8% No
(measured,
not
excluded)
None CBCL – Chinese version -
withdrawn, somatic
complaints,
depressed/anxious subscales
(parent-rated internalising)
Crane et al. 2017 Convenience sample:
children with DCD via
primary schools and charity;
TD via primary schools in
South London, UK.
Confirmed
DCD (medical
report and
researcher
assessment)
30 35 8.61 (7-10) 9.12 (7-10) 70.0% 74.3% Yes (self-
/parent-
report)
None SDQ-Teacher - Emotional
subscale (teacher-rated
internalising)
Davis et al. 2007 Screening of clinical
sample: Cohort of children
born with ELBW or very
preterm in Victoria,
Australia.
Probable DCD
(performance-
based tests)
20 190 NR (8-9) NR (8-9) 75.0% 40.5% No (not
assessed)
None
BASC-parent: internalising
subscale (parent-rated
internalising); BASC-
teacher rated (teacher-rated
internalising)
141
Dewey et al. 2002 Population screening: public
and private schools in
Calgary, Canada.
Probable DCD
(performance-
based tests,
screening
questionnaires)
45 78 11.8 (NR) 11.4 (NR) 55.7% 75.6% No
(measured,
not
excluded)
None CBCL - internalising
(parent-rated internalising)
Francis &
Piek
2003 Population screening:
Grades 3-5 in primary
schools in Perth, Australia.
Probable DCD
(performance-
based test)
42 42 NR (7-11) NR (7-11) 52% 52% No (not
assessed)
Age and
gender
CDI (self-rated depression)
Hill &
Brown
2013 Convenience sample: DCD
adults via support groups
and higher education
institutions.
TD adults via higher
education institutions and
local community centres
across UK.
Confirmed
DCD (medical
report)
36 49 29.28 (19-59) 27.84 (18-56) 42% 49% Yes (self-
report)
None STAI-Trait (self-rated
anxiety); STAI-State (self-
rated anxiety); BDI (self-
rated depression)
King-
Dowling et
al.
2015 Population screening:
community organizations in
Southern Ontario, Canada.
Probable DCD
(performance-
based tests)
37 117 4.92 (NR) 4.92 (NR) 78% 42% No (not
assessed)
None CBCL (parent-rated
internalising)
Li et al. 2018 Population screening:
Participants from the
Physical Health and
Activity Study Team project
from schools in Canada.
Probable DCD
(performance-
based test)
79 1127 13.45 (12-14) 13.40 (12-14) 38.0% 51.6% No (not
assessed)
None Kessler-6 Scale (self-rated
internalising)
142
Missiuna et
al.
2014 Population screening:
Grades 4-8 from schools
within two health boards
regions in Canada.
Confirmed
DCD
(researcher
assessment)
68 91 11.8 (NR) 12.0 (NR) 60% 51% Yes (parent-
/school-
report)
None CDI (self-rated depression);
CDI (parent-rated
depression); SCARED (self-
rated anxiety); SCARED
(parent-rated anxiety)
Piek et al. 2007 Screening of a twin sample:
Monozygotic twins
discordant for DCD on the
Australian Twin Registry.
Probable DCD
(screening
questionnaire)
24 24 11.91 (6.45-
16.99)
11.91 (6.45-
16.99)
45.8% 45.8% Yes
(screening
measure)
Age, gender,
(also genes
and shared
environmental
factors)
Twin and Sibling
Questionnaire - Sad Affect
subscale (parent rated
depression)
Piek et al. 2008 Population screening:
Kindergarten children in a
primary school in Western
Australia.
Probable DCD
(performance-
based tests)
14 26 NR;
Total sample
mean = 4.3
(3.75-5.33)
NR;
Total sample
mean = 4.3
(3.75-5.33)
71.4% NR No (not
assessed)
Noned CBCL - anxious/depressed
subscale (parent-rated
internalising)
Pratt & Hill 2011 Convenience sample: DCD
from support groups,
existing research, schools
within London and south-
east England; TD from
existing research and
schools within London and
south-east England.
Confirmed
DCD (medical
report)
27 35 10.08 (6-15) 9.38 (6-15) 74.1% 51.4% Yes
(medical
report and/or
screening
measure)
None SCAS-Parent (parent-rated
anxiety)
Schoemaker
&
Kalverboer
1994 Population screening: Dutch
mainstream schools.
Probable DCD
(performance-
based test)
18 18 7.3 (6.1-9.0) 7.3 (6.0-9.1) 83.3% 83.3% No (not
assessed)
Age, gender STAIC-Trait (child-rated
anxiety); STAIC-State
(child-rated anxiety)
143
Skinner &
Piek (child
sample)
2001 Population screening:
Primary schools in Western
Australia.
Probable DCD
(performance-
based tests)
58 58 NR (8-10) NR (8-10) 31% 31% No (not
assessed)
Age, gender STAIC-Trait (self-rated
anxiety); STAIC-State (self-
rated anxiety)
Skinner &
Piek
(adolescent
sample)
2001 Population screening: High
schools in Western
Australia.
Probable DCD
(performance-
based tests)
51 51 NR (12-14) NR (12-14) 43% 43% No (not
assessed)
Age, gender STAIC-Trait (self-rated
anxiety); STAIC-State (self-
rated anxiety)
van den
Huevel et al.
2016 Population screening:
Primary schools in middle
and eastern Netherlands.
Confirmed
DCD
(researcher
assessment)
TRF: 20;
SDQ 22
TRF: 307;
SDQ: 339
NR;
For total
sample (not all
included in
analysis): 7.0
(4.3-10.3)
NR
For total
sample (not all
included in
analysis): 7.2
(4.0–10.8)
NR;
For total
sample
(not all
included
in
analysis):
69.6%
NR;
For total
sample
(not all
included
in
analysis):
49.1%
No
(measured,
not
excluded)
None TRF- internalising subscale
(teacher-rated internalising)
SDQ-teacher- Emotional
subscale (teacher-rated
internalising)
Wagner et
al.
2012 DCD: Clinical sample from
occupational therapy groups
in Germany;
TD: elementary schools in
Germany.
Confirmed
DCD
(researcher
assessed)
35 35 7.69 (5-11) NR “matched” 77.1% 77.1% No (not
assessed)
Age, gender IDS – Internalising scale
(parent-rated internalising)
144
Watson &
Knott
2006 DCD: Clinical sample from
Occupational therapy
department in West of
Scotland;
TD: Primary schools in
West of Scotland.
Confirmed
DCD (medical
report)
15 30 10.2 (8-12) 10.25 (NR) 80% 80% Yes (self-
report or
medical
report)
Age and
gender
Birleson Depression
Measure (self-rated
depression)
BASC: Behaviour Assessment System for Children; BDI: Beck Depression Inventory; CBCL: Child Behaviour Checklist; CDI: Children’s Depression Inventory; ELBW: Extremely Low Birth Weight; IDS: Intelligence and Developmental Scales; NR: Not reported; SCARED: Screen for Child Anxiety Related Disorders; SCAS: Spence Chi ldren's Anxiety Scale; SDQ: Strengths and Difficulties Questionnaire; SMFQ: Short Moods and Feelings Questionnaire; STAI: State-Trait Anxiety Inventory for Adults; STAIC: State-Trait Anxiety Inventory for Children; TRF: Teacher Report Form. a Additional confounders included in adjusted analysis: maternal depression, family adversity, IQ, social communication. b Based on reported age for combined male and female subsamples. c Study reports two alternative performance-based measures for determining DCD. Criteria based on the MABC were used for comparability with other studies. d Adjusted for gender and IQ, but unadjusted data used in meta-analysis.
145
Dowling et al., 2015; Missiuna et al., 2014; Piek et al., 2008; Pratt & Hill, 2011;
Schoemaker & Kalverboer, 1994; van den Heuvel et al., 2016; Wagner et al., 2012;
Watson & Knott, 2006). Six studies explicitly excluded DCD participants with ADHD
based on self-/parent-/school-reported diagnoses (Crane et al., 2017; Hill & Brown,
2013; Missiuna et al., 2014; Watson & Knott, 2006) or based on scores on standardised
screening questionnaires (Piek et al., 2007) or either of the two (Pratt & Hill, 2011). The
remaining studies either did not assess for ADHD (Campbell et al., 2012; Davis et al.,
2007; Francis & Piek, 2003; King-Dowling et al., 2015; Li et al., 2018; Piek et al., 2008;
Schoemaker & Kalverboer, 1994; Skinner & Piek, 2001; Wagner et al., 2012) or
measured symptoms but did not exclude those above the clinical cut-off (Chen et al.,
2009; Dewey et al., 2002; Harrowell et al., 2017; van den Heuvel et al., 2016; Wagner et
al., 2016).
All outcome measures of internalising symptoms were based on questionnaires.
Most studies measured overall internalising symptoms using the Child Behaviour
Checklist (Chen et al., 2009; Dewey et al., 2002; King-Dowling et al., 2015a), Strengths
and Difficulties Questionnaire (Crane et al., 2017; Harrowell et al., 2017; van den
Heuvel et al., 2016; Wagner et al., 2016), Behaviour Assessment System for Children
(BASC; Davis, Ford, Anderson, & Doyle, 2007), Teacher Report Form (van den Heuvel
et al., 2016), Kessler-6 (Li et al., 2018), or the Intelligence and Developmental Scales
(Wagner et al., 2012). Nine studies specifically measured depressive symptoms using
the Children’s Depression Inventory (Francis & Piek, 2003; Missiuna et al., 2014), Beck
Depression Inventory (Hill & Brown, 2013), Short Mood and Feelings Questionnaire
(Harrowell et al., 2017), BASC – Depression subscale (Campbell et al., 2012), Twin and
146
Sibling Questionnaire – Sad Affect subscale (Piek et al., 2007), or the Birleson
Depression Measure (Watson & Knott, 2006). Six studies specifically measured levels
of anxiety symptoms using the State-Trait Anxiety Inventory for Children (Schoemaker
& Kalverboer, 1994; Skinner & Piek, 2001), State-Trait Anxiety Inventory for Adults
(Hill & Brown, 2013), Screen for Child Anxiety Related Disorders (Missiuna et al.,
2014), or Spence Children's Anxiety Scale (Pratt & Hill, 2011). Overall, the outcome
measures were based on parent-report in seven studies (Chen et al., 2009; Dewey et al.,
2002; King-Dowling et al., 2015; Piek et al., 2007, 2008; Pratt & Hill, 2011; Wagner et
al., 2016; Wagner et al., 2012), teacher-report in two studies (Crane et al., 2017; van den
Heuvel et al., 2016), self-report in eleven studies (Campbell et al., 2012; Francis & Piek,
2003; Harrowell et al., 2017; Hill & Brown, 2013; Li et al., 2018; Schoemaker &
Kalverboer, 1994; Skinner & Piek, 2001; Watson & Knott, 2006), and a combination in
two studies (Davis et al., 2007; Missiuna et al., 2014).
Risk of bias
The risk of bias in the included studies is summarised in Table 2. Selection bias
was variable. The use of a population screening method in 16 studies ensured the DCD
sample was somewhat representative of the population studied. However, seven studies
recruited the DCD sample from a selective group or convenience sample, which may be
at greater risk of bias. This included children born very preterm or with extremely low
birth weight (Davis et al., 2007), volunteer samples from DCD support groups (Crane et
al., 2017; Hill & Brown, 2013; Pratt & Hill, 2011), monozygotic twin samples (Piek et
al., 2007), or clinical samples from occupational therapy services (Wagner et al., 2012;
147
Watson & Knott, 2006). In most studies, the TD group was drawn from the same
community (e.g. school, geographical location) as the DCD group, except for four
studies that were from a different source (Crane et al., 2017; Hill & Brown, 2013; Pratt
& Hill, 2011; Wagner et al., 2012) and thus had an increased risk from selection bias.
Additionally, while 10 studies confirmed diagnoses of DCD by independent assessment
or clinical reports (Chen et al., 2009; Crane et al., 2017; Harrowell et al., 2017; Hill &
Brown, 2013; Missiuna et al., 2014; Pratt & Hill, 2011; van den Heuvel et al., 2016;
Wagner, 2017; Watson & Knott, 2006), 13 did not confirm key diagnostic criteria
(Campbell et al., 2012; Davis et al., 2007; Dewey et al., 2002; Francis & Piek, 2003;
King-Dowling et al., 2015; Li et al., 2018; Piek et al., 2007, 2008; Schoemaker &
Kalverboer, 1994; Skinner & Piek, 2001; Wagner et al., 2016). Caution should be taken,
therefore, when attributing differences in internalising symptoms in these studies to
DCD. Most studies were cross-sectional and, therefore, unable to account for the
stability of internalising symptoms over time. Of the longitudinal studies, one controlled
for baseline internalising symptoms (Wagner et al., 2016).
The studies varied in the comparability of study groups and control for important
confounders. Age and gender were controlled in 11 studies through either matched
groups (Campbell et al., 2012; Francis & Piek, 2003; Piek et al., 2007; Schoemaker &
Kalverboer, 1994; Skinner & Piek, 2001; Wagner et al., 2012; Watson & Knott, 2006) or
adjusted analyses (Harrowell et al., 2017; Wagner et al., 2016). The study by Piek et al.
(2007) adopted a monozygotic twin design which also controls for a wide range of
genetic and shared environmental factors. The remaining studies failed to sufficiently
148
Table 2. Summary of risk of bias
Study DCD
representative of
population
TD from the
same population
DCD diagnosis
confirmed
Prior internalising
symptoms
controlled
Controls for
gender
Controls for age Standardised
outcome
measure
Sufficient
length of
follow-up
Sufficient
follow-up rate
Campbell et al. (2012, male) * *
* * *
Campbell et al. (2012, female) * *
* * *
Chen et al. (2009) * * * *
Crane et al. (2017) * *
Davis et al. (2007)
*
*
Dewey et al. (2002) * *
*
Francis and Piek (2003) * *
* * *
Harrowell et al. (2017, male) * * * * * * *
Harrowell et al. (2017, female) * * * * * * *
Hill and Brown (2013)
*
*
King-Dowling et al. (2015) * *
*
Li et al. (2018) * * *
Missiuna et al. (2014) * * *
*
Piek et al. (2007)
*
* * *
Piek et al. (2008) * *
*
Pratt and Hill (2011)
*
*
Schoemaker and Kalverboer (1994) * *
* * *
Skinner & Piek (2001, adolescent) * * * * *
Skinner & Piek (2001, child) * * * * *
van den Huevel (2016) * * *
*
Wagner et al. (2012)
* * * *
Wagner et al. (2016) * * * * * * *
Watson and Knott (2016)
* * * * *
149
control for age and gender. Although one such study did adjust for differences in gender
in the analysis (Piek et al., 2008), it also included intellectual ability as a covariate, and
so the unadjusted difference between the groups was used in the meta-analysis to ensure
comparability (Voils et al., 2011).
All studies utilised outcome measures with established validity and reliability
psychometrics. It should be noted that three studies only reported specific narrow-band
depression or anxiety subscales, as opposed to using the broad-band internalising scales
(Campbell et al., 2012; Piek et al., 2008). These might raise concerns around selective
reporting.
Finally, only three studies included a longitudinal follow-up (Harrowell et al.,
2017, male & female sample; Wagner et al., 2016). This was over a year in all three
studies. However, there were high rates of attrition in all three.
Internalising symptoms
Since only one study based on an adult sample was identified (Hill & Brown,
2013), that study was excluded from the remaining analyses to minimise heterogeneity.
Across the 22 studies with children and adolescents, those with DCD or probable DCD
were found to have higher levels of internalising symptoms than TD controls with a
medium effect size (g = 0.61; 95% CI: 0.48-0.74; see Figure 3 for forest plot). There was
significant moderate heterogeneity among the studies (I2 = 56%; χ2 = 47.84; p = 0.0007).
150
Figure 3. Forest plot for total internalising symptoms across all studies
151
Moderator analysis
The results of the moderator analyses are summarised in Table 3. The results
revealed that the effect size was significantly larger in studies that utilised a cross-
sectional design (versus longitudinal), that included a majority male sample in the DCD
group (versus majority female) and that recruited a selective or convenience sample of
participants (as opposed to population-based screening). There was also a trend (p = .05)
towards a greater effect size in studies that did not control for important confounders and
in studies that excluded individuals with a diagnosis of ADHD. No significant effect was
found for publication year, age, confirmation of DCD diagnosis, outcome respondent, or
type of internalising measure.
Sensitivity analysis
A sensitivity analysis was conducted to include only those studies meeting five
or more criteria on the NOS. A moderator analysis identified a significant difference
between the high-quality and low-quality studies (Q = 4.42; p = 0.04). Analysis of the
higher quality studies (k = 10) found a smaller, but still moderate, effect of DCD on
internalising symptoms (g = 0.46; 95% CI: 0.34 to 0.58). There was also no evidence of
significant heterogeneity among these ten studies (Q = 5.95; p = 0.55; I2 = 0%).
Publication bias
The funnel plot (see Figure 4) displayed some asymmetry, with smaller studies
tending to report larger effect sizes, possibly indicative of publication bias. Eggers test
was statistically significant, supporting the presence of publication bias (Egger’s bias =
152
Table 3. Summary of results for moderators
Moderator k Total n g 95% CI Q p
Year of publication
0.31 0.58
- Post-2010 12 3388 0.58 0.39 to 0.77
- Pre-2010 10 1074 0.65 0.49 to 0.81
Design
9.33 0.002
- Longitudinal 3 937 0.29 0.09 to 0.49
- Cross-sectional 20 3645 0.67 0.54 to 0.80
Age
0.02 0.88
- Included adolescents 10 2682 0.60 0.39 to 0.80
- Not included adolescents 12 1780 0.62 0.44 to 0.79
Gender
4.72 0.03
- >50% male 15 1889 0.71 0.52 to 0.91
- >50% female 7 2573 0.46 0.33 to 0.58
Confirmed diagnoses
2.30 0.13
- Confirmed DCD 9 998 0.75 0.48 to 1.01
- Probable DCD 13 3434 0.52 0.39 to 0.65
Population-based design
5.06 0.02
- Population screening 17 4176 0.52 0.41 to 0.62
- Selective sample 4 286 1.02 0.59 to 1.45
ADHD
3.70 0.05
- Excluded ADHD 5 379 0.97 0.53 to 1.41
- Did not exclude ADHD 17 4083 0.52 0.41 to 0.63
Controlled for confounding
3.81 0.05
- Age and gender controlled 12 1752 0.48 0.36 to 0.60
- Age and gender not controlled 10 2710 0.74 0.51 to 0.97
Outcome respondent a
2.18 0.14
- Self-report 10 1907 0.50 0.39 to 0.62
- Parent/teacher-report 12 2396 0.71 0.46 to 0.97
153
Outcome measure type
1.13 0.57
- Total internalising 12 3492 0.59 0.39 to 0.78
- Depression only 5 495 0.54 0.36 to 0.72
- Anxiety only 4 316 0.77 0.38 to 1.16
Sensitivity analyses
Study quality
4.42 0.04
- High quality 10 1638 0.46 0.34 to 0.58
- Low quality 12 2800 0.72 0.51 to 0.93
ADHD: Attention Deficit Hyperactivity Disorder.
a Missiuna et al. (2014) excluded from analysis due to using both self-and observer-report. Inclusion of each type of measure from
this study, independently, did not significantly change the results.
Figure 4. Funnel plot of effect sizes and standard error
154
2.38; 95% CI: 0.20 to 4.56; p = 0.02). However, Duval and Tweedie’s Trim and Fill
procedure did not impute additional studies and, therefore, the effect size adjusted for
publication bias was identical to the non-adjusted effect size. Rosenthal’s Fail-safe N,
suggested that the number of studies with null results that would have to be included to
produce a non-significant combined effect size is 1076. This is substantially larger than
the minimum required when applying Rosenthal’s (1979) formula (i.e. 120).
Discussion
The present systematic review and meta-analysis indicates that children and
adolescents with DCD or probable DCD experience greater levels of internalising
symptoms compared to their TD peers. The magnitude of this difference suggests a
moderate effect size, with individuals with DCD scoring over half a standard deviation
higher. This moderate effect, although reduced slightly, remained robust after excluding
lower quality studies. Publication bias is also unlikely to have substantially influenced
the result. Several methodological and participant factors that may moderate the
magnitude of this effect have also been identified.
DCD and internalising symptoms
The findings are in line with the emerging consensus that DCD can have a
significant impact on an individual’s mental health (Caçola, 2016; Mancini et al., 2016;
Missiuna & Campbell, 2014). Notably, the magnitude of the effect identified is
comparable, if not greater, than that found in meta-analyses of a wide range of chronic
155
physical health conditions including fibromyalgia, cleft lip and palate, migraine
sufferers, diabetes, spina bifida, and epilepsy (Pinquart & Shen, 2011a, 2011b).
The Environmental-Stress Hypothesis was proposed to account for this
relationship between DCD and internalising symptoms (Cairney, Rigoli, & Piek, 2013).
It suggests that the motor impairments in DCD can expose an individual to a variety of
secondary stressors, which over time can lead to poorer mental health. Although
potential mediators were not explored in this review, they have been outlined previously
(Mancini et al., 2016). They include peer victimisation (Campbell et al., 2012), reduced
leisure activities (Raz-Silbiger et al., 2015), impaired social skills (A. Wilson et al.,
2013), poorer self-esteem (Rigoli et al., 2012), physical inactivity (Li et al., 2018),
reduced social support (Rigoli et al., 2017), and lower perceived academic competence
(Lingam et al., 2012). Individuals with DCD may also experience impairments to
various cognitive abilities, including executive functions (Wilson, Ruddock, Smits-
Engelsman, Polatajko, & Blank, 2013) and social cognition (Cummins, Piek, & Dyck,
2005). This may further impact on self-regulation and mental wellbeing (Lantrip,
Isquith, Koven, Welsh, & Roth, 2016; Letkiewicz et al., 2014). Future meta-analyses
regarding the magnitude of the effects for these potential mediators will be important,
providing further opportunities for intervention.
Moderating factors
The present review has identified several methodological factors which might
moderate the degree to which DCD is associated with internalising symptoms. As
expected, the effect size was likely over-estimated in cross-sectional compared to
156
longitudinal studies, and in convenience or clinic-referred samples compared to samples
recruited via population-based screening. Such methodologies have less control of
confounding factors and a less representative selection of DCD participants (e.g. more
severe impairments in clinical samples). There was also a trend towards larger effect
sizes in studies that failed to control for age and gender. Again, the magnitude of the
effect sizes in these studies were likely inflated by confounding (Deeks et al., 2003). No
significant effect was found for the DCD criteria used. This suggests that, although
establishing all DCD diagnostic criteria is important for the quality of research in this
area (Zwicker et al., 2013), failing to do this might not have a substantial impact on the
results. Population-based screening, longitudinal design and control for confounders
should take priority.
Participant factors that might moderate the effect of DCD on internalising
symptoms were also identified. The effect was larger in studies with a majority male
sample. This would suggest that DCD has a greater impact on the mental health of males
and is in line with the findings of Sigurdsson et al. (2002). This is particularly important
given the prevalence of DCD may be greater in males (Kirby & Sugden, 2007;
Missiuna, 1994). It has been suggested that male children attribute greater value to
physical activity and sports compared to females, which might account for the larger
impact of DCD on their wellbeing (Poulsen, Ziviani, & Cuskelly, 2006; Poulsen,
Ziviani, Cuskelly, & Smith, 2007). However, although significant, the difference in
magnitude of the effect sizes were minimal. Additionally, only two of the included
studies reported direct comparisons of the impact of DCD on males and females, with
one suggesting no difference (Campbell et al., 2012) and the other suggesting a greater
157
impact for females (Harrowell et al., 2017). Regardless of which gender experiences the
larger effect, there is evidence that DCD can impact on the mental health of both and
perhaps it is the mechanisms by which this occurs that differ (Li et al., 2018).
There was also a trend towards larger effect sizes in studies that specifically
excluded participants with ADHD. This contradicts what might have been expected
from previous research (Martin, Piek, & Hay, 2006; Missiuna et al., 2014; Rasmussen &
Gillberg, 2000). One possible explanation for this finding is that children with comorbid
ADHD are more likely to be diagnosed and to subsequently receive support for their
difficulties (Heath, Toste, & Missiuna, 2005; Rivard, Missiuna, Hanna, & Wishart,
2011). Participants with DCD only, on the other hand, may have continued through
childhood for a long time with the motor difficulties going unrecognised and
unsupported (Gaines et al., 2008). However, it should also be noted that there were only
five studies included in the meta-analysis that specifically excluded participants with
ADHD. All five studies were also of a lower quality. It is a more plausible explanation
that methodological limitations inflated their combined effect size and, therefore,
caution should be taken when drawing any conclusions about the moderating effect of
comorbid ADHD.
Contrary to what might be expected, no significant moderating effect was found
for age. This is somewhat surprising, given that previous research has suggested the
impact of DCD on internalising symptoms may increase as children transition into
adolescence (Missiuna, Moll, King, King, & Law, 2007; Skinner & Piek, 2001).
However, only one study included in the present review reported separate outcomes for
adolescents and children. The moderator categories for the meta-analysis were based on
158
somewhat arbitrary criteria (i.e. studies that included adolescents in their sample, as
opposed to studies with a pure adolescent sample) which may have prevented the
detection of differences between the age groups.
Finally, no significant effect was found for the type of outcome measure or
respondent, suggesting that DCD may be associated with elevated levels of depression,
anxiety, and overall internalising symptoms, regardless of the person rating it.
Strengths and limitations
There are several limitations of this review that should be considered when
interpreting the findings. First, the quality of the included studies was variable. Most
studies were based on cross-sectional data only, which makes it difficult to establish
causality. Although three longitudinal studies were included, only one controlled for
baseline measures of internalising symptoms and all reported a high rate of attrition.
Many of the studies also failed to control for important confounders (i.e. age and gender)
and to establish all DCD diagnostic criteria.
The moderator analysis should also be interpreted with caution. As outlined
above, there were an insufficient number of studies within some of the moderator
categories to reliably explore their impact (including age and comorbid ADHD). Most of
the studies were also conducted in western, developed countries and, therefore,
generalisation to other countries is limited. Additionally, only one study with adults was
identified and this study failed to meet many of the quality criteria. Therefore, the extent
159
to which elevated internalising symptoms persist into adulthood in people with DCD is
unclear.
However, this review is the first attempt to systematically synthesise the
evidence on internalising symptoms in individuals with DCD and provide a pooled
summary of the effect size. Publication bias is unlikely to have a substantial impact on
the findings. Additionally, despite methodological limitations of the included studies,
potential moderating factors have been identified. The effect size also remained
substantial, and heterogeneity reduced, after excluding lower quality studies.
Implications and conclusion
Despite some limitations, the findings of this review have important clinical and
research implications. It can be concluded that individuals with DCD may have an
increased risk of developing elevated levels of internalising symptoms. The difference of
half a standard deviation between individuals with DCD and their peers could be
considered clinically important (Norman, Sloan, & Wyrwich, 2003). This would support
the practice of routine screening of mental health difficulties in individuals with DCD
and motor impairment. Given that DCD is poorly understood among professionals
(Gaines et al., 2008; B. N. Wilson et al., 2013) and that families often report difficulties
obtaining support (Stephenson & Chesson, 2008), such routine screening could be useful
across a range of services (including schools, occupational therapy, physical healthcare,
and mental healthcare). The findings also highlight the need for professionals in mental
health services to be aware of the disorder and how it impacts their patients.
Additionally, the findings support the need for the development of psychosocial
160
interventions for DCD with a focus on the secondary stressors that might mediate the
link between motor difficulties and emotional wellbeing (Missiuna et al., 2012).
Future research should focus on high-quality longitudinal studies to better
understand the causal link between DCD and internalising symptoms, including the role
of important mediators. It is recommended that studies include probability sampling
strategies and control for confounders and the stability of internalising symptoms over
time. This review has also highlighted the need for more research investigating mental
health in adults with DCD, especially given that the impact of DCD has been found to
continue into adulthood, including negative effects on higher education, employment
and mental wellbeing (Cousins & Smyth, 2003; Hill et al., 2011; Kirby, Williams,
Thomas, & Hill, 2013). Research investigating the effectiveness of routine screening for
mental health difficulties in DCD and psychosocial interventions would also provide
insight into the improved management of DCD. Given the major economic impact of
poor mental health (Trautmann, Rehm, & Wittchen, 2016) and the increasing focus on
improving psychological wellbeing in government policy (Department of Health, 2011),
the need to identify and support those individuals most at risk of mental health
difficulties is crucial.
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Appendix: Guidelines for authors
[Appendix removed for E-Thesis submission]
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Part 3: Summary of Clinical Experience
Adult placement
Service: Community Mental Health Team
Dates: October 2015 – September 2016
Experience: Conducting psychological assessments and interventions with adults
presenting with a range of mental health difficulties. I predominantly worked within a
Cognitive-Behavioural Therapy (CBT) model. This included CBT for depression,
generalised anxiety disorder, social anxiety, obsessive compulsive disorder, health
anxiety and panic disorder. I gained experience applying third-wave CBT models (e.g.
Acceptance and Commitment Therapy) in one-to-one sessions and facilitating a
Dialectical Behaviour Therapy (DBT) group for people diagnosed with borderline
personality disorder. I gained some experience administering neuropsychological tests. I
also conducted a service evaluation of a multidisciplinary referrals meeting.
Child and adolescent placement
Service: Tier 2 Child and Adolescent Mental Health Team
Dates: October 2016 – March 2017
Experience: Working within a Choice and Partnership Approach to conduct
psychological assessments and intervention with young people presenting with mild-
moderate mental health difficulties and their families. I predominantly worked within
the CBT model with some experience applying systemic models. Presenting concerns
included depression, anxiety and behavioural difficulties. I gained experience working
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with young people with Attention Deficit Hyperactivity Disorder and Autism Spectrum
Conditions. I facilitated a CBT group for anxiety. I administered neuropsychological
tests. I had the opportunity to conduct consultation work for local schools and provided a
teaching session to health professionals on Developmental Coordination Disorder.
Older people placement
Service: Memory Assessment Service
Dates: April 2017 – September 2017
Experience: Conducting detailed cognitive assessments and formulations with adults
presenting with possible dementia. I gained experience administering and scoring a
range of neuropsychological tests and working within a neurocognitive model to assist
with diagnosis. I delivered brief interventions with people adjusting to a recent diagnosis
of dementia and their carers. This included one-to-one, family, and group sessions
focused on psychoeducation, CBT, systemic therapy, neurorehabilitation, and cognitive
stimulation therapy. Presenting diagnoses included Alzheimer’s disease, vascular
dementia, frontotemporal dementia, Lewy-bodies dementia, Parkinson’s disease,
progressive supranuclear palsy, and mild cognitive impairment. I also delivered a
training session to the multidisciplinary team on delivering a diagnosis of dementia.
People with Learning Disabilities placement
Service: Community Team for People with Learning Disabilities
Dates: October 2017 – March 2018
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Experience: Adapting psychological models and interventions for adults with a learning
disability. This included working within an integrated framework, informed by CBT,
systemic, neurocognitive, and behavioural models. Presenting concerns included low
mood, anxiety, anger, and behaviours that challenge. I gained experience conducting
functional assessments and developing Positive Behaviour Support plans to help clients
and their carers manage challenging behaviours. I gained experience with consultation
and joint working with other professionals. I also conducted relaxation groups within an
inpatient service. I had the opportunity to supervise assistant psychologists.
Specialist placement: Neuropsychology
Service: Epilepsy neuropsychology outpatients / inpatient acute traumatic brain injury
Dates: April 2018 – September 2018
Experience: Conducting neuropsychological assessment with people with a diagnosis of
epilepsy. This included individuals concerned by cognitive difficulties or as part of a
presurgical screening assessment. I gained experience working within the
neurocognitive model and writing detailed neuropsychological reports. I also worked in
an inpatient acute neurorehabilitation service for people with a traumatic brain injury. I
gained experience with neuropsychological assessment; delivering brain injury
education groups; working with families; conducting mood assessments and
intervention; delivering insight-raising interventions; and introducing cognitive
rehabilitation strategies. I obtained experience working closely with other healthcare
professionals, taking on a leadership role within the team, and supervising assistant
psychologists.
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Part 4: Table of Assessments Completed During Training
Year I Assessments
ASSESSMENT TITLE
WAIS WAIS Interpretation (online assessment)
Practice Report of
Clinical Activity
A cognitive-behavioural assessment and initial
formulation of a female in late adolescence experiencing
anxiety, low mood, and non-epileptic seizures
Audio Recording of
Clinical Activity with
Critical Appraisal
Audio recording and critical appraisal of a Cognitive
Behaviour Therapy session with a male with depression
and social anxiety
Report of Clinical
Activity N=1
A cognitive-behavioural assessment and intervention for
a man in his twenties experiencing depression and social
anxiety
Major Research Project
Literature Survey
Mental health in Developmental Coordination Disorder:
Literature Survey
Major Research Project
Proposal
Executive function and internalizing problems in
children with and without Developmental Coordination
Disorder
Service-Related Project Clinicians’ views on a weekly meeting dedicated to
discussing new referrals in a Community Mental Health
& Recovery Service
Year II Assessments
ASSESSMENT TITLE
Report of Clinical
Activity/Report of
Clinical Activity –
Formal Assessment
A neuropsychological assessment of a male in his mid-
teens, presenting with academic and behavioural
difficulties at school
PPLD Process Account A reflective process account of a trainee’s experiences of
a Personal and Professional Development group during
the first two years of training
Year III Assessments
ASSESSMENT TITLE
Presentation of Clinical
Activity
A post-diagnostic intervention for a woman in her 70’s
recently diagnosed with vascular dementia: A cognitive-
behavioural and systemic approach
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Major Research Project
Literature Review
Internalising symptoms in Developmental Coordination
Disorder: A systematic review and meta-analysis
Major Research Project
Empirical Paper
Internalising symptoms and executive function
difficulties in adolescents with and without
Developmental Coordination Disorder
Report of Clinical
Activity/Report of
Clinical Activity –
Formal Assessment
An assessment and intervention with a man with learning
disabilities and a cavernous haemangioma presenting
with challenging behaviour: A positive behavioural
support approach
Final Reflective
Account
On becoming a clinical psychologist: A retrospective,
developmental, reflective account of the experience of
training