Analyses were performed using the SPSS statistical package, version 19.0 (IBM, Armonk, NY). Variables were first checked for distributional assumptions. Multicollinearity was assessed and the Variance Inflation Factor for all independent variables and covariates (i.e., deviant peer affiliation, OPRM1 genotype, parental monitoring, age, and sex) was less than 2, indicating acceptable statistical associations between explanatory variables. A series of t-tests and χ2 tests compared the two groups on AUD diagnostic status, deviant peer affiliation, and parental monitoring. To test whether the association between the candidate gene and the development of an AUD was influenced by specific environmental circumstances, a backward stepwise logistic regression equation was conducted. The dependent variable was the binary categorization of AUD diagnosis as the presence (1) or absence (0) of either alcohol abuse or dependence. Predictors were the candidate gene (coded as AG/GG versus AA), the moderators (i.e., deviant peer affiliation, parental monitoring), and the candidate gene × moderator interactions. Continuous independent variables (deviant peer affiliation, parental monitoring) were centered prior to being entered into the models. Potential confounding effects of sex and age were controlled
