Our results should be interpreted in the context of their limitations. First, the participants in our two samples were of European descent, the latter exclusively of Finnish descent, which may limit the generalizability of the present findings to samples from the same ancestral background. Second, although our association and moderation findings were in the expected direction, the effect sizes were quite small—often accounting for less than 1% of the variance. Although there is much enthusiasm for personalized medicine approaches [50] that use genome-wide information to identify for whom and under what conditions prevention and intervention efforts are likely to be effective, our results caution against using empirically-derived GWAS scores in a clinical setting for complex behavioral outcomes such as alcohol problems due to the fact that they account for a limited proportion of the variance [51]. Third, alcohol problems in FinnTwin12 were assessed at age 14. Accordingly, endorsements of alcohol problems at this age may represent a more severe phenotype than those at age 18 in ALSPAC. The age and measurement differences across the ALSPAC and FinnTwin12 samples may explain,
