One end goal for this area of research is the identification and understanding of causal environmental influences on genetic effects as targets for prevention and intervention efforts. The selection of environmental features for G–E studies should consider fundamental conditions for causality including statistical association, time order of relationships, and whether there are other plausible explanations65. Particularly relevant to this topic are gene-environment correlations as alternative explanations for a GxE effect5. A classic example is the correlation between genetic susceptibility for alcohol use and the selection into a deviant peer group56. At the community level, a related phenomenon is the selection of people who drink heavily into more disadvantaged areas over time66, which is likely to happen in addition to neighborhood causal effects on heavy drinking and AUD. To rule out alternative explanations in GxE studies, it is therefore advantageous to select environmental features that are exogenous to the individual and that exclude individual choice whenever possible.
