We first conducted preliminary analyses to examine descriptive statistics and correlations between study variables using SPSS 25.0. ANOVA analyses were also conducted to examine mean differences in social support and alcohol use across developmental stages. All analyses were stratified by ancestry. To test our hypotheses, we conducted a series of hierarchical linear regression analyses using Mplus version 8.3 separately for EAs and AAs. We included participants’ age, sex, educational attainment, and household income as covariates in all analyses. We first examined the main effects of alc-PRS on alcohol use (Model 1). Next, we added social support from family and friends as additional predictors to the regression model to examine main effects of family and friend support simultaneously (Model 2). To examine interaction effects between alc-PRS and family/friend support, we added product terms of alc-PRS and mean-centered family and friend support as additional predictors to the regression model (Model 3). We also examined potential gene-environment correlations (rGE) by testing correlations between alc-PRS and family/friend support. Significant rGE were accounted for in our models testing G×E effects by specifying alc-PRS and family/friend
