complete, comparison group (see footnotes in Table 2). Table 2A comparison of academic attainment between the national NPDa sample and ALSPAC children who have enrolled, have recently participated or are lost to follow-upALSPAC enrolment and current participation statusComparative indicatorNational NPD KS4 GMEa samplebEnrolled in ALSPACcNo recent participationRecently participateddEligible for future follow-upLost to attritionAcademic attainmentat the age of 16 yearse n1 759 17411 0085473553594521556 Mean score308317287347324278 IQR (25–75)266–374280–380242–350314–398290–380224–350aNPD 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
