Our study has several limitations. First, our participants included only individuals of European-American descent. We selected a homogenous sample in order reduce GWAS false positives due to population stratification; however, the GWAS weights we used to calculate the externalizing disorder polygenic scores in the present study may have limited generalizability as a result. This is because GWAS findings across a number of complex traits from individuals of European ancestry do not replicate in individuals of African ancestry (Marigorta & Navarro, 2013); relatedly, recent findings from alcohol dependence GWAS implicate the same alcohol-metabolizing pathways and genes in African- and European-Americans; however the specific genetic variants differ across populations (Gelernter et al., 2013). Thus, the GWAS weights used to create the polygenic scores in the current study may not be appropriate for constructing externalizing disorder polygenic scores in samples of diverse ancestry. Second, although we find evidence for our hypothesized main and interactive effects, they only account for a small amount of the variance. Third, we relied on a modest set of self-report measures of the parenting and peer environments, and incorporating
