We ran a family-based GWAS using the GWAF package (Chen & Yang, 2010) on the adult subsample (n = 1,249), which accounts for familial nesting and genetic distance using a kinship matrix. Covariates included gender, age at interview, and cohort. We then used GWAS estimates to calculate polygenic scores for the adolescent and young adult prospective participants using the --score procedure in PLINK (Purcell et al., 2007), which computes a linear function of the number of score alleles an individual possesses weighted by the associated GWAS t-statistic.
