To probe for the OPRM1 effects reported above, all analyses were repeated incorporating alcoholism severity as a covariate. All the findings reported above remained statistically significant when severity was added to the models. In order to control for population stratification effects, all models were repeated in Caucasians only (n = 30) and the results supported the original findings both in magnitude and direction. For Stimulation, there was an OPRM1 × Alcohol interaction (β = −9.46, SE = 4.37, t = −2.17, p< .05). For Vigor there was an OPRM1 main effect (β = 0.85, SE = 0.35, t = 2.45, p< .05) and an OPRM1 × Alcohol interaction (β = −0.34, SE = 0.15, t = −2.29, p< .05). And for Positive Mood, there was an OPRM1 main effect (β = 0.98, SE = 0.33, t = 3.03, p< .01) and an OPRM1 × Alcohol interaction (β = −0.49, SE = 0.15, t = −3.26, p< .01). Further, given the genotype group differences on smoking status, all analyses were repeated while controlling for current smoking status. Doing so resulted in
