Analysis of covariance (ANCOVA) models analyzed the principal component score for the placebo-adjusted adaptive response as the dependent variable, with family history of alcoholism, recent drinking history, and SNP genotype as potential main effects. Gender was included as a covariate. Due to the a priori hypothesis that family history, recent drinking history and genotype variation would contribute to the adaptive response, all main effects were included in the final model. All 2-way interactions between the main effects and gender were tested. Other interactions and covariates were included in the final model only if significant (p<0.05). Separate analyses were performed for each SNP, modeling genotype as an additive effect.
