that genetic influences were stronger in environments characterized by higher rates of migration in and out of the municipality; conversely, shared environmental influences predominated in local communities characterized by little migration. We also found that genetic predispositions were stronger in communities composed of a higher percentage of young adults slightly older than our age-18 Finnish twins and in regions where there were higher alcohol sales. Further, the magnitude of genetic moderation observed in these models that allowed for variation as a function of a quasi-continuous environmental moderator was striking, with nearly a fivefold difference in the magnitude of genetic effects between environmental extremes in some cases.
