Covariates included in all analyses were sex, and 10 ancestry principal components. Sex was assessed using a single binary item in each study. Analyses in the COGA and Add Health samples included birth year as a covariate to control for generational birth cohort differences. All participants from ALSPAC were born in 1991 or 1992. Age at assessment was calculated from date of birth (Table S2). Covariates in COGA also included genotyping array, and in early adulthood and adulthood, individual proband status. We did not include age as a covariate because the aim of this study was to examine genetic effects in different age groups and because of the of the potential for collinearity between age at assessment and birth year.
