Another issue with the detection and interpretation of gene-environment interaction effects involves the range of environments being studied. For example, if we assume that the five levels of the environment shown in Figure 1b represent the true full range of environments that exist, if a particular study only included individuals from environments 0–2, it would conclude that there is a fan-shaped gene-environment interaction. Belsky and colleagues (2009) have suggested this may be particularly problematic in the psychiatric literature because only in rare exceptions (Bakermans-Kranenburg & van Ijzendoorn 2006, Taylor et al. 2006) has the environment included both positive and negative ends of the spectrum. Rather, the absence of environmental stressors has usually constituted the “low” end of the environment, e.g., the absence of life stressors (Caspi et al. 2003) or the absence of maltreatment (Caspi et al. 2002). This could lead individuals to conclude there is a fan-shaped interaction because they are essentially failing to measure, with reference to Figure 1b, environments –2 and –1, which represent the positive end of the environmental continuum. In looking at Figures 1a and
