These results should be interpreted in the context of seven potentially important methodological limitations. First, we used regression rather than structural equal modeling in our analyses. We used regression models because they allowed us to easily incorporate data on parental psychopathology in our measures of genetic risk and because of their greater simplicity, flexibility and ease of interpretation. However, as we have used them, they are less precise in their ability to separate genetic from familial environment effects. Our measures of genetic risk could include environmental parental influences, although a prior study from this cohort showed no evidence of environmental transmission of risk for AUDs from parents to children (Kendler et al. 1994). In constructing our measures of genetic risk, we weighted contributions from MZ twins twice as strongly as from DZ twins, thereby protecting ourselves from any shared environmental influences ‘leaking into’ our measures of genetic risk.
