Detailed descriptions of recruitment and assessment procedures from this multi-site study can be found in previous publications (Gelernter et al., 2014, Gelernter et al., 2013). The sample consisted of small nuclear families originally collected for linkage studies and unrelated individuals. Briefly, subjects were interviewed using the Semi-Structured Assessment for Drug Dependence and Alcoholism (SSADDA) to assess symptoms of drug use and other major psychiatric disorders (Pierucci-Lagha et al., 2005, Gelernter et al., 2005). MaxDrinks was assessed with the question “In your lifetime, what is the largest number of drinks you have ever had in a 24-hour period, including all types of alcohol?” The number of drinks was coded as standard drinks. We used log-transformed MaxDrinks (LogM) values to represent MaxDrinks in the analysis models. A total of 2,328 EA and 3,215 AA subjects had MaxDrinks data. The mean of LogM was 2.95+/-0.84 in the EA sample, and 2.57+/-1.01 in the AA samples. The LogM in AAs was significantly lower than in EAs (p < 0.0001). The distributions of LogM for EA and AA samples are shown in supplemental Figure 1.
