Two statistically independent alcohol consumption phenotypes were examined: any intake (drinker/non-drinker status) and the regular quantity of alcoholic drinks consumed per week as a quantitative trait (drinks/week). Both phenotypes were assessed based on the Research Program on Genes, Environment, and Health (RPGEH) survey. On this survey, participants were asked regarding the past year: “On average, how many days a week do you have a drink containing alcohol?” (no days, 1 day, 2 days, 3 days, 4 days, 5 days, 6 days, or every day). Further, participants were asked: “On a typical day that you drink, how many drinks do you have?” (none, 1, 2, 3, 4, 5, 6, 7, or ≥8). Individuals who reported drinking ≥ 1 day per week and ≥ 1 drink per day were defined as ‘drinkers’, whereas those who provided negative answers (“no days” and “none”) were considered as ‘non-drinkers’. For alcohol drinkers, the regular quantity of alcohol drinks consumed per week was calculated by multiplying the two answers. Because this quantitative measure of quantity of alcoholic drinks consumed per week was positively skewed, we performed a log transformation prior to conducting genetic association analyses.
