The current analyses predict alcohol use, but not volume or frequency. We chose this measure because drinking, regardless of level, by 9th grade is related to increased risk for a range of problem behaviors in adolescence and later alcohol problems in young adulthood (Pikanen et al., 2005). Future cGxI analyses of the PROSPER data set will no doubt focus on other alcohol outcomes, included but not limited to volume and frequency of drinking in later adolescence and problem drinking in young adulthood. In addition, it would be very useful to follow-up the most compelling finding of this study—that OXTR risk interacts with intervention status to impact the selection of risky peers—with longitudinal analyses. The current study focused on 9th grade outcomes as peers are especially relevant (Steinberg & Monahan, 2007) and drinking appears especially harmful during this time. Because PROSPER has longitudinal data on peer affiliations across each grade from 6th to 12th grade, it provides the opportunity to investigate not only what genes impact peer affiliation, but also when different genes impact these affiliations.
