Table 2.

A comparison of academic attainment between the national NPD^a sample and ALSPAC children who have enrolled, have recently participated or are lost to follow-up

	ALSPAC enrolment and current participation status
Comparative indicator	National NPD KS4 GMEa sampleb	Enrolled in ALSPACc	No recent participation	Recently participatedd	Eligible for future follow-up	Lost to attrition
Academic attainmentat the age of 16 yearse
n	1 759 174	11 008	5473	5535	9452	1556
Mean score	308	317	287	347	324	278
IQR (25–75)	266–374	280–380	242–350	314–398	290–380	224–350

^aNPD KS4 GME: The National Pupil Database (NPD) ‘Key Stage 4’ (KS4) dataset records, pupil census and assessment data for all pupils in English schools at the mean age of 16 years. ALSPAC has linked 14 878 ‘eligible’ children to a subset of the NPD KS4 records that relate to government-maintained establishments (GME). This NPD KS4 GME sample has a 89.5% coverage of all English pupils nationally and 84.3% regionally (the area including and surrounding the cities of Bristol and Bath). The NPD GME excludes privately funded and specialist care establishments and as such offers the best available, yet not complete, comparison group. The majority of the remaining ALSPAC ‘eligible sample’ whom we have not linked to the NPD KS4 GME are thought to live outside England or relate to individuals where there is insufficient information to establish accurate linkage.

^bAll pupils, excluding those in ALSPAC, from English GMEs who sat their KS4 assessments during the same academic years as the ALSPAC cohort (academic years 2007–09).

^cAll pupils, from English GMEs, who are from families that have enrolled in ALSPAC by completing an ALSPAC questionnaire or clinical assessment.

^dAll pupils, from English GMEs, who completed an ALSPAC assessment in the ‘transition to adulthood’ phase (completed a ‘CCS’ or ‘CCXC’ questionnaire or attended the TF17 Focus clinical assessment).

^eAcademic attainment at the age of 16 years (total points score for the pupils eight highest scoring assessments).