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 ALSPAC questionnaire or clinical assessmentNational NPD KS4 GME sampleaEnrolled in ALSPACbOdds ratioCharacteristicCategoryn/n (%)n/n (%)OR (95% CI)P > chi2‡Child sexFemale871 375/1 770 654 (49.21)5470/11 008 (49.69)1.02 (0.98–1.06)0.313Child ethnicityWhite1 508 926/1 744 429 (86.50)10 505/10 933 (96.09)3.85 (3.50–4.24)<0.001Low household incomeFSMc218 033/1 745 353 (12.49)682/10 959 (6.22)0.46 (0.43–0.50)<0.001aAll 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).bAll pupils, from English GMEs, who are from families that have enrolled in ALSPAC by completing an ALSPAC questionnaire or clinical assessment.cEligible for ‘free school meals’ (FSM), indicating a joint parental income of ≤£16 000.7 ‡Chi-squared test for homogeneity (equal odds). Table 4A comparison of socio-demographic characteristics between those children who did and did not participate in the 16–18-year data collection assessmentsEnrolled in ALSPACaRecently participatedOdds ratioCharacteristicCategoryn/n (%)n/n (%)OR (95% CI)P > chi2‡Child sexFemale5470/11 008 (49.69)3181/5535 (57.47)1.88 (1.74–2.03)<0.001Child ethnicityWhite10 505/10 933 (96.09)5322/5508 (96.62)1.34 (1.10–1.62)0.004Low household incomeFSMb682/10 959 (6.22)240/5519 (4.35)0.51 (0.44–0.60)<0.001aAll pupils, from
