Next, we conducted a secondary series of analyses to examine whether our pattern of results was robust when controlling for divorce/separation, college attendance, gene-by-covariate and covariate-by-environment interactions, and family ascertainment status. First, the original model was fit after removing participants who reported divorce or separation (n = 36) from the sample. This allowed us to rule out the possibility that our observed effects were due to the inclusion of divorced/separated individuals in the unmarried group in view of evidence that divorce and separation are associated with greater alcohol problems (Grant et al., 2015; Kessler, Walters, & Forthofer, 1998). Second, we fit a variation of the original model including college attendance as a time-varying covariate. College students engage in more heavy episodic drinking compared to their non-student age-matched peers (Johnston, O’Malley, Miech, Bachman, & Schulenberg, 2015; O’Malley & Johnston, 2002; Slutske, 2005), so controlling for college attendance allowed us to examine whether our observed effects were driven by college attendance. Third, to address concerns that gene-by-environment effects may be confounded by the effects of gene-by-covariate and covariate-by-environment interactions (Keller, 2014), we
