Comparisons (Table 2) show that those children in the ALSPAC ‘enrolled sample’ have a higher educational attainment at the age of 16 years than the NPD KS4 GME national sample, a difference that is not present when comparing the ALSPAC ‘eligible sample’ (mean attainment score of 309, data not shown) with the NPD KS4 GME national sample. This difference in mean attainment increases with increasing completeness of participation in ALSPAC; conversely children who have not recently participated or are lost to follow-up through study attrition have a lower educational attainment than the national average. The ALSPAC ‘enrolled sample’ (Table 3) are more likely to be White and less likely to be eligible for free school meals than the NPD KS4 GME national sample. Recent responders (Table 4) are more likely to be female, White and less likely to be eligible for free school meals, whereas those lost to attrition (Table 5) are more likely to be male and eligible for free school meals. Table 3A comparison of socio-demographic characteristics between the National NPD sample and children who have completed any
