The SRE consists of 4 items; for the current study, each item referred to the first five or so times a participant used alcohol. Participants were asked to report the number of standard drinks they consumed before they experienced signs of alcohol’s effect (from feeling any effect of the alcohol on to slurring words, feeling unsteady on their feet, to unwanted falling asleep). Responses were winsorized to account for outliers. Consistent with prior papers, responses were winsorized to limit extreme values and reduce the effect of possibly spurious outliers. SRE scores were calculated by summing drinks needed for effects across items and dividing by the number of the up to four effects experienced, as recommended by Schuckit and colleagues (Schuckit et al., 1997). The final score was used as a continuous outcome in subsequent GWAS.
