development of functional movement scale for infants

7/28/2019 Development of Functional Movement Scale for Infants

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J O U R N A L O F A P P L I E D M E A S U R E M E N T , 3 ( 2 ), 1 9 0 -2 0 4Copyright 2 0 0 2 D E V E L O P M E N T O F A F U N C T IO N A L M O V E M E N T S C A L E F O R I N F A N T S 19 1

Development of a FunctionalM ovement Scale for InfantsSuzann K. Campbell

University of Illinois at ChicagoBenjamin D. WrightJ. Michael Linacre

University of Chicago

The increasing survival rate of infants with a complicated birth and perinatal higenerated the need for a test of functional motor performance with the capabilityidentifying children under four months of age with delayed dev elopment which could'addressed with physical therapy. This paper describes a Rasch analysis of the psychomequalities of the Test of Infant Motor Performance (TIMP) for the purpose of reducinglength of the test while maintaining its precision as a measurement device. Folioanalysis of fit statistics, item-to-total correlations, redundancy of item difficulty mealand consideration of clinically-relevant features of test items from analysis of 17 32the TIMP was reduced from 59 to 4 2 items forming a functional motor scale for premaborn infants. The resulting person separation index was 4 .85 and the item sepindex was 23.79.

Req uests for reprints should be sent to Suzann K. Campbell, Department of PhTherapy, University of Illinois at Chicago, 1919 W. Taylor Street M/C 898, Chica60612-725 1, email. skc @uic.edu .

An increasing number of infants with perinatal complications now survive as aresult of advanced technology and caregiving interventions provided in specialcare nurseries. The developmental morbidity associated with this trend, how-ever, appears to be unchanging (Fanaroff, Wright, Stevenson, Shankaran,Donovan, Ehrenkrans, Younes, Korones, Stoll, Tyson, Bauer, Oh, Lemons, Papile,and Verter, 1995). For example, infants with brain insults (Pinto-Martin, Whitaker,Feldman, V an Rossem, and Paneth, 200 0) or chronic lung disease (Majnemer,Riley, Shevell, Birnbaum, Greenstone, and Coates, 2000), and those born ex-tremely early tend to have delayed motor development (McCormick, McCarton,Tonascia, and Brooks-Gunn, 1 99 3) Improving the accuracy with which infantsat risk for disability are identified remains a challenge, in part because infantscan recover from some neurodevelopmental abnormalities during the first yearof life (Wildin, Smith, Anderson, Swank, Denson, and Landry, 19 97). Thepurpose of this paper is to describe the use of Rasch analysis in the developmentof a test of functional motor performance intended to identify infants whos emovement capabilities demonstrate delayed development. The specific goal ofthis analysis was to reduce the length of the test.

T h e T es t o f In f an t M ot or P er f orm an ceThe Test of Infant Motor Performance (TIMP) is a 25- 35 m inuteassessment of the posture and selective control of mov ement needed byinfants under four months of age for functional performance in daily life.The TIMP was developed to 1) identify infants with delayed motor devel-opment, 2) discriminate among infants with varying degrees of risk forpoor motor outcome, and 3) measure change resulting from intervention.The TIMP has gone through three research versions to date.V ersion 1 of the TIMP was developed by G irolami for use in assessingthe effects on posture and movement of physical therapy provided to prema-ture infants at risk for movem ent dysfunction in a special care nursery(Girolami and Campbell, 1994). The test included fifteen dichotomous itemsthat were scored on the basis of observing infants' spontaneous movements.A n example of these Observed Item s is one used to assess the infant's abilityto hold the head centered along the midline of the body, i.e., keep the headfrom falling to the side while backlying. Twenty-eight additional ElicitedItems were scored on Likert-type scales reflecting the infant's responses tobeing placed in various positions or stimulated with interesting sights andsounds, such as a rattle or the examiner's voice. Results of a controlled

clinical trial demonstrated that the TIMP was a valid tool for capturing theeffects of intervention (G irolami and Campbell, 199 4).


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D E V E L O P M E N T O F A F U N C T I O N A L M O V E M E N T S C A L E F O R IN F A N T S 1 9 392A M P B E L L , e t a l .Based on the sensitivity of TIMP sco res for detection of interven-tion effects, the decision was made to expand the test in order to increasethe age range to include performance of premature infants as young as 32weeks postconceptional age, i.e., 2 months prior to expected date of birth,as well as infants up to 3-4 months of age (chronologic or corrected forpremature delivery). The resulting V ersion 2 of the TIM P had 27 dichoto-mous O bserved Items and 30 E licited Items scored with rating scales. Therating scales for some TIMP items allow one to assess whether or howmuch of an activity an infant can do w hile others are used to assess changesin how an infant solves a mov ement problem, i.e., changing patterns ofmovement synergies used in response to stimulation.

With funding from the Foundation for Physical Therapy, TIMP V er-sion 2 was studied in a cross-sectional sample of 137 infants from threerace/ethnicity groups in the Chicago metropolitan area: non-Latino/a white,black (African or African-American), and Latino/a (Mexican or PuertoRican) (Campbell, O sten, Kolobe, and Fisher, 199 3; Campbell, Kolobe,O sten, Lenke, and Girolami, 1995 ). Data from 174 tests on these subjects,was analyzed with BIGSTE PS V .2.2. Clarity of the measure as reflectedin the item separation index was 7 .38 (root mean square error=0 .19) witha separation reliability of .98. The items separated the infants into about 6levels of ability (person separate index of 6.02 with root mean square er-ror=0.21) which was thought to be excellent in view of the 5- 6-monthrange of the test. TIMP performance correlated with age at r =(Campbell, Kolobe, O sten, Lenke, and Girolami, 19 95 ).

A fter study of R asch analysis results on TIMP V ersion 2 and a reviof new literature on possible predictors of abnormal outcome, the test deopers honed their theoretical understanding of what the T IMP shouldcomplish and made several new changes to the test. As a result, V ersionthe TIMP was developed which included 28 O bserved Items and 31 E liItems, 6 of which were the same items but used to test different sides obody so that asymmetry of movement could be assessed.V arious aspects of the TIMP 's validity were explored in researgraduate students or with funding from the N ational Center for MReh abilitation Research of the National Institutes of Health. V.3TIMP was shown to 1) relate to movement demands on infants proby caretakers in n aturalistic interactions such as bathing, dressing, ,

by maturation and to differentiate among groups of infants with cliff

degrees of risk for poor motor outcome based on medical conditions(Campbell and Hedeker, 20 01), and 3) predict 12-month outcome on theAlberta Infant Motor Scale with high sensitivity and specificity (Campbell,Kolobe, Wright, and Linacre, in press). Prediction to 5-year outcome iscurrently under study ( Kolobe and B ulanda, personal communication).Despite strong support for the proposed uses of the TIMP resulting

from our research, a shorter tool was de sirable for practical clinical use.The purpose of this paper is to present evidence from Rasch analysis ofTIMP V .3 data and to describe how R asch item fit statistics and otherconsiderations were used to shorten the test to create V ersion 4.M e t h o d s

SubjectsThe subjects in this study were a sample of convenience born during theyears 199 6-98 and recruited from the special care nurseries of three hospitals or

from the com munity within the Chicago metropolitan area. Subject recruitmentmethods were approved by the Institutional Review Board for the protection ofthe rights of human subjects at the University of Illinois at Chicago (#H-9 9-115 8) and at each field testing site. Subjects were 15 9 infants with a range ofmedical complications who participated either in a study of test-retest reliabilityover the space of three days (n=56) or in both the test-retest and a longitudinalstudy (n=103) of performance on the TIMP. Fifty-five percent of the infantswere male, 42% female (3% had missing data on sex). The distribution of race/ethnicity was 38% white, non-Latino/a; 31% black (African or African-Ameri-can); 26% Latino/a; and the rest Asian (1% ), mixed (1% ), or missing (3% ).Procedures

With the informed consent of a parent to test an eligible subject andmedical clearance from the infant's physician, the infants in the longitudi-nal study were scheduled for testing with the TIMP every week until ap-proximately 4 months corrected age. The number of weekly tests eachinfant received ranged from 2-23 . Test numbers varied because of 1) ageand health status of the infant at recruitment, 2) illness, and 3) familyscheduling conflicts. In the test-retest study, infants were tested twicewithin the space of 3 days.At initial testing, infants were required to be off mechanical ventila-

tion and cleared for testing by their physician, but could be receiving oxy-


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D E V E L O P M E N T O F A F U N C T I O N A L M O V E M E N T S C A L E F O R IN F A N T S 1 9 594A M P B E L L , e t al .gen by nasal canula. Thus infants began testing at different ages based onhealth. The infant was tested in its current environment: isolette with vitalsigns monitors in place, open crib, home, o r occasionally during an outpa-.tient clinic visit. Testers were not told the age or m edical history of theinfant before testing (unless information was needed to guarantee safehandling of an infant during assessment). Testing occurred about one hourprior to expected feeding time for preterm infants or about mid-way be-tween feedings for older infants.

Twelve testers participated in this study. Each tester had experienceda period of training in use of the TIMP which consisted of a 4-hour wo rk-shop on development and validation of the test and how to score it, inde-pendent reading of research on the test, practice in testing at least 10 infants of varying ages, and rating of item performances on 14 v ideotapes of in-fants of different ages with or without a variety of medical complications.Rater consistency was evaluated with the Facets computer program forRasch psychometric analysis (Linacre, 1988); raters needed to have fewerthan 5% misfitting ratings, i.e., unexpected ratings given the infant's leveof ability on an item and the item difficulty, in order to qualify for being atester in this study.Data Analysis

Scores on the TIMP were subjected to Rasch analysis using theBIG STE PS computer program V er. 2.65 in order to transform the raw ordinal scores into interval-level logit measures (Wright and Linacre, 199Wright and Masters, 19 82). A ccording to the Rasch model, the probaity of passing an item is based only on the ability of the subject and thdifficulty of the item and its various scale levels. Analy sis yields bopopulation-independent estimates of item parameters, and individuality estimates for the latent trait being measured (H ambleton, 2000 ), in tcase functional motor performance in early infancy.

The R asch analytical rating scale model was the A ndrich model, bwith each Elicited Item conceptualized as having its own rating scale struture as in the Master's partial credit model. The partial credit model wselected because the rating scale for each E licited Item is unique and tnumber of levels varies from 5 to 7. G iven their dichotomous natO bserved Items were assumed to form a group as a whole. BIGSTEbegins with a central estimate for each person measure, item calibratioand rating scale step calibration. An iterative version of the no rmal a

proximation algorithm is used to reach a rough conv ergence to the ob-served data pattern. The unconditional maximum likelihood me thod, us-ing proportional curve fitting, is then iterated to obtain more exact estimates,standard errors and fit statistics. The scale mean for item difficulty was setto 50 with one logit (log-odds unit) equal to 10 points.Item fit to the Rasch mod el was investigated using infit (informa-

tion-weighted fit statistic which is sensitive to unexpected behav ior af-fecting responses to items near the person's ability measure) and outfit (anoutlier-sensitive fit statistic sensitive to unexpected behavior by personson items far from the person's ability level) m easures. Fit statistics arereported as mean square residuals which have approximate chi-square dis-tributions. In BIG STE PS values of standardized fit statistics are obtainedfrom the squared residuals by means of an asymptotic normal distribution(Windmeijer, 19 90) . Mean-square fit statistics of 1.2 or greater were usedas the cutoff for identifying misfitting items for further evaluation. V aluesbelow one w ere not addressed in the analysis.Items with unsatisfactory fit to the Rasch mod el were reviewed forthe possibility of removal from the test or revision to improve item fit.Before consideration of remo ving any misfitting item from the test, sev-eral factors other than Rasch results were also considered. E licited Itemswere compared with data on frequency of occurrence as a naturalistic de-mand for m ovement during caregiver-infant interactions so that no itembelieved to be of functional significance in daily life would be rem ovedwithout considering whether the item could instead be revised to improveitem response characteristics. Second, how well therapists and parentsliked these items was considered; item deletion was supported by findingthat the items were hard to administer, seemed particularly demanding forfragile infants, or otherwise were difficult for parents to understand basedon therapists' impressions of parent and child responses. A final consid-eration was whether removal of an item would be likely to decrease testprecision because its item difficulty was not duplicated by o ther items atthe same level of scale performance. A finding of redundancy in difficultywith another item was also grounds for consideration of deleting an item.A goal of the analysis was to reduce the number of items, if possible, inorder to minimize infant stress and fatigue and to increase the practicalityof using the test by reducing the time required to administer it.


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DEVELOPMENT OF A FUNCTIONAL MOVEMENT SCALE FOR INFANTS 19 7Resu lts

Testing in the longitudinal study and the test-retest reliability studyresulted in data from 172 3 tests crossing the entire range of age from 32weeks postcon ceptional age through 4 months post-term. O nly the firsttest of a test-retest pair was used in the data analysis. Tests from 1719non-extreme scoring individuals were assessed. The mean Rasch measurewas 55.43 w ith a SD of 10.49 and mean SE of 1.98 with a SD of .45.O verall infit mean square for persons was .98 and outfit mean square was1.10. The person separation index was 4.57 with a reliability of .95.A wide range of item difficulty w as achieved with an item separationindex of 21 .37 and reliability of 1.00. The m ean item measure (as set forthe analysis) was 50 .00 w ith a SD of 11.92, m odel error of .48 with a SD

Table 1Difficulty Calibrations, Infit and Outfit Mean Square Values, and Point BiserialCorrelations for Items Misfitting the Rasch Model*

ITEMIFFICULTY INFITMNSQ OUTFITMNSQ PT.BISERIAL02 Head turn L 55 1.13 1.23 .3003 Head turn R 55 1.15 1.24 .2 904 Hands together 58 1.19 1.27 .2 405 R Hand to mouth 46 1.45 2.23 -.1006 L Hand to mouth 50 1.44 1.89 -.0307 Mouths R hand 72 1.19 1.38 .1908 Mouths L hand 73 1.17 1.36 .2009 Individual R finger movements 37 1.23 1.71 .05010 Individual L finger movements 39 1.26 1.78 .02011 R wrist movements 37 1.11 1.29 .18012 L wrist movements 37 1.11 1.30 .18015 Pelvic lift in supine 43 1.23 1.55 . 12016 Hip/knee flexion 20 1.04 1.38 .10017 R ankle movements 29 1.06 1.28 .17018 L ankle movements 30 1.06 1.31 .17023 Arm movements with forearm off surface 53 1.33 1.47 .10024 Arm movements with upper arm off surface 45 1.26 1.46 .12E3 Straighten spine with head supported 47 1.55 2.26 .40Ell R neck rotation 47 1.06 1.35 .59E13 Defensive head movements 28 1.46 7.90 .10E14 Defensive arm movements 61 1.31 1.35 .56E28 Arm release in prone 57 1.58 1.53 .49E29 Standing 62 1.21 1.17 .58;g* Bold lettering indicates value exceeding the targeted range for item fit statistic of 1.2,

of .23. T he third column from the left in Figure 1 shows that the averageitem difficulties ranged from 20 to 83 (D represents dichotomously scoredO bserved Items and X's represent scaled Elicited Items). Calibrations forthe easiest step on Elicited Items extend the range of the scale down to 10(Fig. 1, second column) w hile calibrations for the hardest step extend thescale up to 85 (Fig. 1, fourth column) Point biserial correlations for itemsranged from -.10 to .78 w ith 29 of 59 (49 % ) greater than .50. Infit meansquare for items was 1.01 with an outfit of 1.21 .

Information on misfitting items is presented in Table 1 . The identi-fied items had difficulty values ranging from 20 to 73 and point biserialcorrelations ranging from -.10 to .59. R eview of the infit mean squaredata for each item revealed 12 items with infit greater than 1.2: 5 E licitedI tems (E3, E 13, E 14, E 28, and E29) and 7 O bserved I tems (05, 06, 09,MEASURE

MAP OF INFANTS AND ITEMS MEASURE100.0 100.0

90.0 90.0

XX80.0 . xxxx 80.0. # XX X. # XX X.## XXX.### XXX.### XX X70.0 .##### # # # x 70.0.##### # # # # xx XX XXD60.0 . # # # # # # # # XD 60.0# # # # # # # # XX########## XXXDD. # # # # # # # # # # # DD. # # # # # # # # # # XXXD########### XX XXX50.0 . # # # # # # # # # XXDDD 50.0############# XX. # # # # # # # # # XXXXXX. # # # # # # # # XXXDD.### # # # D# # # # # #40.0 .### XXXX 40.0# DXX Xxxxxx

DDDDx

30.0 XXXx DDx 30.0XXX XXXXx20.0 xxxxxxx

20.0

10.0 x 10.0INFANTSTEMS-LOWTEMS-MEANTEMS-HIGH

EACH '#' IN THE INFANT COLUMN IS 10 INFANTS; EACH '.' IS 1 TO 9 INFANTSFigure 1. TINIP BIGSTEPS-Version 3 Item Scaling Properties

19 6A M P B E L L , e t a l .


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D E V E L O P M E N T O F A F U N C T I O N A L M O V E M E N T S C A L E F O R I N F A N T S 1 9 998A M P B E L L , e t al .010, 015, 023, and 024). Of the 12, 11 items also had unacceptableoutfit statistics. In addition, 11 items-02, 03, 04, 07, 08, 011, 012,016 , 017 , 01 8, and E ll-had outfit values greater than 1 2Based on these results, the following O bserved Items were deleted informing V .4 of the TIMP: 02 through 08, 011, 012, 01 5, 023, and 024.With the exception of 07 and 08, other items with similar average diffi-culty levels as the items deleted were already available in the scale. Withrespect to 07 and 0 8 with difficulty measures of 72 and 73 , respectively,although other items of similar average difficulty are lacking in this abilityregion, the rightmost column o f Figure 1 shows that several Elicited Itemshave their highest step level in this region . Thus precision at the h igherability levels should be maintained without 07 and 08. Finally, pointbiserial correlations for all removed O bserved Items were low (< .31).

Items 020, 021, and 022 were also deleted, although their fit stalltics were satisfactory, because during testing they engender a positichange from supine to prone that w as an undesirable disturbance dunspontaneous movement observation, and because they w ere redundantdifficulty with reliably obtained E licited Items E2 4, E 26, and E 27 whiassess the same movements under conditions of stimulation.

O f the misfitting Observed Items, only 09, 010, 0 16, 017, and 0were retained. 09 and 01 0 are used to assess the ability to perform invidual finger movements. Their misfit values were just above 1.2 (1.and 1.26 , respectively). They were relatively easy movements for infto display (difficulty 37 and 39 , respectively) in an area of the scale wfew items of similar average difficulty so deleting them might reduceprecision of the scale for the lowest functioning infants. In addition thedelicate finger movements were items that fascinated parents when pointout by testers. Observed Item 0 16 is used to measure kicking and waseasiest item in the test with no other items of similar difficulty. 016's iwas satisfactory and kick ing is a fundamental movement sk ill that thethors believed should be retained in the test. 017 and 01 8 are usedassess isolated movements of the right and left ankle, respectively, ageasy items that were not redu ndant in difficulty with other items.values were satisfactory so the items w ere retained.

O f the five Elicited Items selected for possible revision or deletifrom the TIMP because of high infit values, E3 and E 28 were removed,addition to support for deleting these items based on misfit statistics,were items deemed by therapists to be ones families liked less well

others and both often resulted in crying. Although the point biserial valuefor E 3 w as moderate at .40, neither item was identified as being similar tocaretaker demands for movement in Murney and Campbell's study (19 98)of the ecologic relevance of TIM P E licited Items. O ther items were avail-able with similar difficulties so remo val did not seem likely to affect theprecision of the test.Items El 3, E 14, and E 29 w ere not removed but were instead revised,in part because each of them was found to occur moderately or frequentlyoften in naturalistic interactions (Murney and Campbell, 1998). Problemswith E 1 3, one of the easiest items in the test, were believed to come frominfrequent use of several response categories and little variation in infantperformance, leading to an exceptionally high outfit value (7.90) and poorpoint biserial value (.10 ). R ather than removing the item from the test, itwas revised by collapsing two levels, making the item a 4-level rather than5-level item, and by changing the time allowed for the response to occur tomake it a more difficult item.E 14 had a point biserial correlation of .56 and w as not redundantwith other items in average difficulty. The item, therefore, was revised tocombine the old steps 2 and 3 into one step, leaving a 5- rather than 6-levelitem.E29 is a relatively difficult item (difficulty measure 62) that is used toassess supported standing, an activity therapists believed could not be removedfrom the test because virtually all infants are placed in supported standing bytheir parents (91 % in the study of ecologic relevance of TIMP E licited Items),making it important in daily life interactions. E29's point biserial correlation of.58 also favo red keeping the item but revising it to better reflect what infantsactually did during item administration. To accomplish this task, v ideoclips ofthe standing item from 55 infant observations were reviewed by an experiencedtester. She proposed changes to the item that reflected the infant performancescaught on videotape and the item descriptions were revised.Finally, item E ll with a poor outfit was not removed because an-other item used to test the same activity on the opposite side of the body(E 12) had excellent fit statistics and E ll's point biserial correlation of .59favored keeping the item. Items that wo uld be capable of reflecting asym-metry of performance on the two sides of the body were believed to beimportant items to retain because of their possible diagnostic value.The resulting V .4 of the TIMP has 42 items-13 O bserved Items and29 E licited Items-6 of which are tests of the same activity on either side


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D E V E L O P M E N T O F A F U N C T I O N A L M O V E M E N T S C A L E F O R I N F A N T S 20 100A M P B E L L , e t al .of the body. A fter deleting the 17 selected items from the test, a newBIG STE PS analysis was run using the 42 items of V.4 (before revision ofrating scale descriptions of items E1 3, E 14 , and E2 9). The resulting sum-mary statistics demonstrate that deletion of these items shortens the lengthof the test but does no t significantly change the q uality of the measuringdevice. The mean Rasch measure increased to 57.58 with a SD of 13.05and mean SE of 2.34 with a SD of .64. O verall infit mean square forpersons increased slightly to 1.01 and o utfit mean square to 1.14. Theperson separation index improved to 4 .85 w ith a reliability of .96.

A gain, a wide range of item difficulty w as demonstrated with an itemseparation index of 23.7 9 and reliability of 1.00 . The mean item measure(as set for the analysis) was 50.00 with a SD of 13.49 , model error of .47with a SD of .25. Item difficulties ranged from 2 0 to 87. P oint biserialcorrelations for items ranged from .01 to .81 with 28 of 42 (67% ) greaterthan .50. Infit mean square for items was 1.02 with an outfit of 1.35.Review of the infit mean square data for each item revealed that 5

items remained with infits greater than 1.2: 09 (1.35 ), 010 (1.39), E 13(1.63), E 14 (1 .57), and E 29 (1 .37), all items previously identified and pur-posely not removed from the test. As previously mentioned, E13 , E 14and E 29 have been revised with the expectation that they will perfobetter in data analyses with a new sample of infants. 09 and 01 0 will bretained for the reasons previously given and because further reanalysiremoving these items did not produce substantial improvement in Rascfit statistics for the test as a whole. Thirteen items remain with high outfistatistics. Although these could perhaps be deleted without affecting toreliability or precision, they are items w hich assess mea ningful activitiethat therapists wish to have included for the purposes of obtaining a fulleunderstanding of infant developm ent for use in treatment planning ananticipatory guidance of families regarding their infant's development.Discussion

Rasch analysis was used to reduce the length of a new assessmentinfant posture and movement. The 42 -item TIMP has high precision, gofit to the Rasch psychom etric model, and good fit to the ability levelsinfants tested in the age range for which the test is intended, especial!those with low to moderately high levels of ability (measure ability ranfrom 10 -85 ). The lack of a floor effect indicates sufficient room forsessment of low functioning infants, a major purpose of the examinatio

Harder items would need to be added if precision was desired for 4-month-old infants of the highest ability. This is not the test developers' intent,however, because o ther tests are available for assessing infants from 3-4months of age onward while no other quantitative assessment is currentlyavailable with precision for assessing infants' functional motor perfor-mance under the age of 3 months.With the elimination of 15 items from the set of O bserved Items,many of w hich involved arm and hand functions, it becomes more obviousthat the TIMP is an assessment primarily of gross (large muscle), ratherthan fine, motor function. It is likely that the m isfit of these items re-flected the fact that they are part of a different construct than that of pos-ture and movem ent needed for e arly functional activities or that it is tooearly in life to reliably assess hand and arm functions. Unfortunately,removal of the large number of items that were O bserved Items did little toreduce the physical demands of the TIM P no r the time required for testingbecause O bserved Items do not involve handling Reducing the number ofO bserved Items from 28 to 13, how ever, does reduce the attentional de-mand of the tester because these items must be observed for throughoutthe examination. In addition, one position change was d eleted and re-moval of tw o E licited Items contributes slightly to reducing the time re-quired fo r testing. Future research will assess the feasibility of using asmaller set of the best items as a screening test and for assessment of themost fragile infants.Because we are aware of no other test for young infants that wasdeveloped using R asch analytic methods, we have no other comparabledata to evaluate relative to our results. In general, however, other tests fornewborns and premature infants have a small range o f age, are not inter-

val-scaled, and have not been studied with longitudinal assessment of in-fants to document a linear relationship between age or ability and testscores. Neither do they provide the capability to scale individual items toidentify difficulty level of steps involved in learning various tasks andhow they should appear in the sequence of early development of prema-turely born infants.Scales developed with R asch methods are available for older chil-dren with disabilities (Coster, Ludlow, and Mancini, 19 99 ), including theGross M otor Function Measure (GMF M). A recent report of the use ofRasch analysis to reduce the number of items in the G MFM showed that a

66-item test was as sensitive to change w ith age in children with cerebral


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20 2A M P B E L L , e t a l. D E V E L O P M E N T O F A F U N C T IO N A L M O V E M E N T SCALE FOR INFANTS 203palsy as the earlier 88-item test, but the criteria used to delete items wnot reported (Russell, A very, Rosenbaum, R aina, Walter, and Palisan2000).Along w ith evidence that the TIMP discriminates among infants baseon early medical complications (Campbell and Hedek er, 200 1), predictdevelopment at 12 months from TIM P assessment at 3 months (CampbelKolobe, Wright, and Linacre, in press), and has ecologic validity for asensing activities that are important in daily life (Campbell and Murne199 8), the evidence provided by R asch analysis provides support for thvalidity of the TIMP for use in clinical practice and research to measurethe development of m otor skills in early infancy. The next stage in deveopment of the TIMP will use V .4 for a re-assessment of the test's scalinproperties in a population-based sample of 1200 infants selected to matethe race/ethnicity distribution of the population of low -birth-weight ifants in the U.S. U se of data from this cross-sectional sam ple in a neRasch analysis will alleviate the limitations of the current data obtainefrom repeated assessment of about tw o-thirds of the infants. Data frothe national sample will also be used to establish age standards for perfomance of infants in 14 d ifferent age groups in support of its use as a dianostic measure of infant motor development.

AcknowledgmentsResearch w as conducted at the University of Illinois at ChicagMedical Center, the University of Chicago Hospitals, and Lutheran General Hospital, Park R idge, IL, with funding (R01 HD 3 256 7) from theNational Center for Medical Rehabilitation R esearch of the National In-stitute of Child Health and H uman Development, USP HS. We are grate-

ful to the physicians at each institution--Nagamani Beligere, Jaideep Singand David Sheftel for providing access to their patients. The authorwould like to thank Dolores Schorr, Pat Byme-Bowens, Dawn KuerschneCarrie Ryan, and Kathy Tolzien for assistance in recruiting subjects; BeO sten, Kathy Kamm, P ai-jun Mao Liao, Vinod Subramonian, and SriraBalachandran for assistance with data management; and Betty BrameMary Carter, Judy Hegel, LouAnn Gouker, Thubi Kolobe, Maureen LenkPai-jun Mao Liao, G ail Liberg, Mary Murney, Beth O sten, Celina WisMartin, and Laura Zawacki for testing of infants. Without the participa-tion of infants and their parents who believed that our research would helpother families, this work would not have been possible.

ReferencesCampbell, S. K., and Hedeker, D. (200 1) V alidity of the Test of Infant MotorPerformance for discriminating among infants with varying risk for poor motoroutcome. Journal of Pediatrics, 139, 546-551.Campbell, S. K., Kolobe, T. H. A., O sten, E.T, Lenke, M., and Girolami, G.L.(199 5). Construct validity of the Test of Infant Motor Performance. Physical

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J O U R N A L O F A P P L I E D M E A S U R E M E N T , 3 ( 2 ) , 2 0 5 - 2 3 1C o p y r i g h t 2 0 0 2

Detect ing and Evaluat ingthe Im pact o f M ult id imens ional i tyusing Item F it Statist ics and P rincipalCom ponent A nalys is o f Res idualsE verett V . Smith, Jr.

The University of Illinois at Chicago

The purpose of this research is twofold. First is to extend the work of Smith (19 92, 19 96)and Smith and Miao (199 1, 19 94) in com paring item fit statistics and principal componentanalysis as tools for assessing the unidimensionality requirement of Rasch models. Secondis to demonstrate methods to explore how violations of the unidimensionality requirementinfluence person measurem ent. For the first study, rating scale data were simu lated torepresent varying degrees of m ultidimensionality and the proportion of items contributingto each component. The second study used responses to a 24 item Attention DeficitHyperactivity Disorder scale obtained from 317 college undergraduates. The simulationstudy reveals both an iterative item fit approach and principal component analysis ofstandardized residuals are effective in detecting items simulated to contribute tomultidimensionality. The methods presented in Study 2 d emonstrate the potential impactof multidimensionality on norm and criterion-reference person measure interpretations.The results provide researchers w ith quantitative information to help assist w ith thequalitative judgment as to whether the impact of multidimensionality is severe enough towarrant removing items from the analysis.

Requests for reprints should be sent to E verett Smith, University of I llinois at Chicago,1040 West Harrison Street, M/C 147, Chicago, IL, 60607, e-mail [email protected] .

development of functional movement scale for infants

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