Univariate twin models were fitted to raw data on ever drinking, timing of first alcohol use, AUD, C-RA, and A-RA to attribute variance in these measures to additive genetic (A), shared/familial environmental (C), and individual-specific environmental (E) sources.32 When the alcohol and religious attendance variables were significantly correlated, this correlation was also decomposed into its genetic and environmental sources using bivariate twin models. Additive genetic (A) influences reflect the additive effect of all genetic loci shared identical-by-descent. Shared environment (C) reflects those factors that make members of twin pairs similar to each other (eg, similar family practices), while individual-specific environment (E) refers to those factors that are unique to each member of the twin pair (eg, individual trauma exposure) as well as measurement error. Evidence for A is derived from the MZ correlation (rMZ) being larger than the DZ (rDZ) correlation. Evidence for C arises from rDZ > ½ rMZ, while support for E is based on rMZ < 1. All our results are based on formal model-fitting procedures where raw data were fitted using full information maximum likelihood estimation
