Study subjects were young adult (mean age 24.3 years) males (66.9%) and females (33.1%), who were primarily Caucasian (72.4%) and were non-smokers (93.7%) or light smokers (< 2 days/week). There were no significant differences in demographic variables across genotype groups or subgroups with the exception of significant effects of self-reported race on the distribution of OPRM1 genotype, and OPRM1 × DAT1 subgroups (Table 1a, b). As shown in Figure S1, the distribution of AIM component scores (C1, C2) for individual subjects and self-reported race revealed three population clusters which generally aligned with the three primary self-reported race categories (Caucasian/white, African American/Black, and Asian). Since some individuals C1, C2 coordinates differed from their self-reported race, C1, C2 values were included in all statistical models to adjust for genetic race/ancestral differences.
