We used partial Pearson correlations, controlling for sex, to test associations between the FinnTwin12 polygenic scores and alcohol problems. We used moderated multiple regression to test our gene-by-environment interaction hypotheses that parental knowledge and peer deviance would moderate the predictive association of polygenic scores with the age 14 alcohol problems measure. For these analyses, the parameters of interest were the statistical interactions between the environmental factors (parental knowledge and peer deviance) and the polygenic scores. The main effects of sex and the environmental factors were used as covariates in the relevant models. Parental knowledge, peer deviance, and polygenic scores were centered on their means prior to running moderation analyses to reduce co-linearity among predictor variables.
