Our study had several limitations, including a modest target sample size (target N = 1,167, discovery sample size N = 162,082; given the current sample size and a significance level of α = 0.05, our study had 80% power51 to detect an effect size of R2 ≥ 0.0068.). Further replication studies in larger, independent samples are warranted. Also, the current analyses were restricted to individuals of European ancestry, so we cannot confidently extrapolate our conclusions to other populations. Third, COGA is ascertained for genetic liability to addiction, which may have influenced findings. Our “high” group (16%) is somewhat larger than those noted in two prior general-population longitudinal studies6,8 but similar to one study that oversampled for tobacco4 smoking and lower than a study with overrepresentation of individuals from high-crime neighborhoods7. Thus, similar classes have been noted, although there is much variability in their class size. Fourth, while self-report of perceived peer use is commonly studied, and does not significantly differ from actual peer use52, it is possible that it is less objective than reports by peer nominees53. Furthermore, as we
