The emerging genetics literature suggests that the small sample sizes (e.g., n<1000), typical of candidate gene studies to date, are likely to be grossly underpowered for detecting genetic influences with small effect sizes. (The reason that many, perhaps most, candidate gene studies report positive associations despite such lack of power is discussed below.) Some of the confusion about expected effect sizes and the sample sizes needed for cGxE studies may surround differences in the conceptualization of GxE effects across different fields (see Figure 2 for an illustration of this). Candidate GxE studies can be conceptualized in two ways: (1) as a genotype moderating the association between an environmental factor and an outcome (i.e., increasing exposure to major stressful life events is more strongly associated with an increased risk for depression in the presence of the short allele of 5HTTLPR; often the default conceptualization for psychologists) or (2) as an environment moderating the association between a genotype and an outcome (i.e., the association between the short allele of 5HTTLPR and depression is strongest in individuals experiencing major stressful life events; often
