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Matching PLASCand ALSPAC
PLASC/NPD User Group Workshop13th September 2006
Andy Boyd([email protected])
David Herrick([email protected])
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What is ALSPAC?
“Avon Longitudinal Study of Parents and Children”
Cohort study of children and their parents, based in south-west England
Designed to determine ways in which the individual’s genotype combines with environmental pressures to influence health and development
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Study design
Eligibility criteria: Mothers had to be resident in Avon and have an expected date of delivery between 1st April 1991 and 31st December 1992
Avon was broadly representative of the UK as a whole and has a relatively stable population
Enrolled sample of 14,541 pregnancies resulting in 14,062 live born children
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Data
Self Completion Questionnaires Hands on Measurements Biological Samples Health Records Education Records Direct School Contact
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ALSPAC at School
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Educational Data - Primary
Contact with ~350 primary schools in the four local LEAs:• Bristol• South Gloucestershire• North Somerset• Bath and North East Somerset
Private & special schools included Parental contact for out of area cases
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Educational Data - Primary
Questionnaires in Year 3 & Year 6:• School (Head teacher)• Class (Class teacher)• Child (Class teacher)
Year 4 test: Maths Year 6 tests: Maths, Spelling,
Science
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Educational Data - Secondary
Questionnaire for maths teachers in 2002/3 (Year 7) & 2004/5 (Years 7, 8 & 9) and associated class lists
Year 6 maths test repeated in Year 8 Moving away from direct school
contact
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Educational Data - SATS
Entry Assessment & KS1 data on eligible children at local schools acquired directly from the LEAs
Linkage to NPD:• Increased coverage• Easier linking (UPN)• PLASC as well
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Study Approval & Cohort Matching
Ethics & study approval The Fischer Trust Validating the cohort match Anonymizing the data set Issues encountered
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Ethics & Study Approval
ALSPAC Ethics & Law committee LREC (NHS research ethics committee)
‘Eligible’ vs. ‘Enrolled’ cohort Final research file to be anonymous DfES commissioned a third party,
The Fischer Trust, to conduct the cohort/data match
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The Fischer Trust
An intermediately between ALSPAC and the DfES
FT received both ALSPAC and NPD datasets and conducted the cohort match.
FT created it’s own ID (however we were also provided with UPN)
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Cohort match variables
Details for 20551 children provided: Child Surname Child Forename Child Date of Birth Home Postcode School Indicator (name & address) from
ALSPAC schools data collection
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Validating the cohort match
For our methodology, study requirements we wanted to reverse check the match
FT matched 86% cases provided (17671 cases)
Very few errors found (<0.5%)
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FT matches by variable
FT 'match level' variable
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Problems with the match variables
Child Surname (change over time) Child Forename (familiar names) Child Date of Birth Home Postcode (out of date and lost
cases) School Indicator (name & address) from
ALSPAC schools data collection (depended on school participation and out of date information)
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Anonymizing the data set
UPN transferred to new internal ID and then to new collaborator ID
Personal variables dropped (DoB, names, postcode, age at census)
Identifying variables dropped (care authority)
Variables recoded (ethnicity, SEN) LEA & Estab Ids recoded into our own
unique ALSPSCHL_ID
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Issues encountered
Cases not covered by NPD REE – not including old schools Primary to junior succession Children who resit years or are in a
non natural school year Historical records of school
movement
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Issues - UPN
We discovered that the U in UPN isn’t that unique!
215 ALSPAC cases have multiple UPNs (with no clear pattern as to why)
PLASC 2004 has two ALSPAC children with the same UPN
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Sample
At least 1 PLASC return identified for 11,997 (85%) of the 14,062 enrolled live births:• 2002 - 11,850 (84%)• 2003 - 11,731 (83%)• 2004 - 11,473 (82%)
Balance:• Private schools• Home educated• Outside England• Not identified
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Supplied Documentation
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ALSPAC & PLASC
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Editing (1)
Convert string variables to numeric, label and sort missing values and write documentation.
Calculate age at census. From date of entry derive age on starting
at current school and length of time at current school.
Derive expected NCYG (National Curriculum Year Group).
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Editing (2)
Ethnicity: 39 cases had new ethnicity codes in 2002 – these were mapped back to old codes and an equivalent to main category derived. Also derive white/non-white indicators.
Care: In 2003 17 of the 34 cases marked as currently in care were marked as N for ever in care. Did not occur in 2004.
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Unanswered questions
6.6% of children were not in the expected NCYG in 2002 compared with 0.7% in 2003 and 2004.
Large increase in use of code T for ethnicity source between 2003 & 2004, even if restricted to Year 7 only.
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Ethnicity Source (1) 2003 2004
N % N %
C Child 625 3.8 968 6.1
P Parent 12418 76.1 9998 62.5
S Current school 3178 19.5 2530 15.8
T Previous school 17 0.1 2354 14.7
O Other 89 0.5 150 0.9
16327 16000
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Ethnicity Source (2) 2003 (Yr 7) 2004 (Yr 7)
N % N %
C Child 534 13.8 472 5.2
P Parent 2517 65.1 4956 54.6
S Current school 796 20.6 1229 13.5
T Previous school 5 0.1 2326 25.6
O Other 17 0.4 89 1.0
3869 9072
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Age on starting current schoolPLASC 2002
26 2 17571
6984
736 731
5034
1222 988
171
0
1000
2000
3000
4000
5000
6000
7000
8000
0 1 2 3 4 5 6 7 8 9 10
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Illegal Values (1)
Numeric codes in Boarder field (should be only ‘B’ or ‘N’) – 2 cases in 2002, 7 in 2003 and 13 in 2004.
Code ‘1’ in for NCYG in 2003 for child in secondary school who was expected to be in Year 7 and who was recorded as in Year 6 in 2002 and Year 8 in 2004.
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Illegal Values (2)
X in NCYG in 2004 – 2 cases. A small number of cases are missing
important fields like date of entry, NCYG.
3 cases had the same code for primary and secondary SEN types.
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Uses Identifying Developmental Impairments:
• Investigating the use of early life parental questionnaires to predict later problems.
• SEN types used to identify autism, speech/language problems and possible learning difficulties.
• Twin approach with medical database searches.
Autism project. Ethnicity.
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Wish List
Detailed documentation describing how different fields relate (especially for SATs).
Numeric fields supplied as numeric rather than string.