perceived peer alcohol use. This is accomplished by including causal pathways in both directions in a subset of our models (available in the Supplementary Material). A critical implication of causal processes is that, if the expressed phenotype changes, the downstream phenotype will be impacted. In contrast, if only genetic/environmental correlation is at play, factors that modify one’s own alcohol use will not necessary impact the alcohol use of one’s peers. Elucidating the mechanistic etiology of alcohol consumption and peer alcohol use – causal or otherwise - could potentially improve prevention and treatment efforts in that the impact of external social processes and that of genetic/environmental factors can be explicitly evaluated and, in some cases, modified.
