As is true of all statistical interactions, GxE are most easily detected under circumstances where the interaction term and genetic and environmental main effects are not correlated (Cohen, Cohen, West, & Aiken, 2003). When genetic factors influence exposure to risk or protective environments, a gene-environment correlation (rGE) is created (Plomin, DeFries, & Loehlin, 1977). This is particularly relevant for alcohol research because parents who are heavy drinkers often create environments that increase risk for problematic alcohol consumption by their children (e.g., due to poor parenting style, marital dissolution, or economic hardship). Although results from extended pedigree studies suggest that rGE contributes a minimal amount of variance to drinking (Eaves et al., 1989), even a small rGE has the potential to influence conclusions about GxE (Albert, Ratnasinghe, Tangrea, & Wacholder, 2001; Liu, Fallin, & Kao, 2004).
