characteristics collected at ages 11.5 and 13 years. Alcohol use outcomes were assessed at age 15.5. The number of individuals with data for each of the above measures analyzed in this project is shown in Table 1. There were 12,647 individuals with data available on at least 1 time point: 6,504 (51%) of these individuals were male, and 6,143 (49%) were female. The majority of the sample (86%) was white (reflecting the relative homogeneity of the region from which the sample was drawn), 4% reported another ethnicity, and 10% of the sample had unknown ethnicity. There was considerable variability with respect to educational level: 3,482 (28%) of mothers had less than O level education (Ordinary Level; exams taken at the completion of legally required school attendance, equivalent to the present UK General Certificate of Secondary Education), 4,991 (40%) had O level education, and 3,703 (29%) had A level (Advanced Level; exams taken at age 18 years) or university education, with 471 missing. Full details of all measures, procedures, sample characteristics, and response rates are available at www.alspac.bris.ac.uk. Ethical approval for the study was obtained from the ALSPAC Ethics and Law Committee and the Local Research Ethics Committee.
