The observed shared environmental correlation (rC) indicates that those family-level factors (or other environmental factors which increase the similarity of both members of a twin pair) that increase one’s own drinking also impact alcohol-based peer affiliation. The influence of shared environmental factors – on SELF and PEER themselves, and on their covariation – decreases from adolescence into young adulthood. Thus, in adulthood, genetic correlation rather than shared environmental liability accounts for the majority of covariation.
