We evaluated whether variation in sample characteristics (age, gender, nationality), and methodological features (study design, variation in predictors and outcomes) covaried systematically with 5-HTTLPR genotype GxE findings. Negative findings appeared to loosely correspond to sample size, participant age, quality of stress assessment and severity of drinking outcomes. While the four studies that used younger subjects, smaller samples, and broader measures of drinking behaviors found significant GxE (Covault et al., 2007; Kaufman et al., 2007; Nilsson et al., 2005; Laucht et al., 2009) two studies with older subjects, larger samples, limited measures of SLEs, and more severe alcohol-related outcomes did not find evidence for GxE (Dick et al., 2007b; Du & Wan, 2009). While this may indicate that GxE decreases over the course of development or across stages of alcohol consumption, inconsistency in evidence for GxE may simply result from poorer measurement quality of stressors in studies with larger samples sizes. Few researchers tested whether males and females differed in alcohol-related GxE, and results were inconsistent across studies (Table 3).
