Second, although the idea that there are genes that confer sensitivity to one’s environment is appealing, there are important measurement issues that make it difficult to make a priori claims that a particular variant operates as a differential susceptibility locus (meaning that a genotype confers risk in a negative/risky environment but is associated with especially good outcomes in a positive/protective environment; Belsky et al., 2009). The difficulty in classifying variants as differential susceptibility loci lies in the fact that our measures of the environment do not have a true zero. Thus, in a low-risk sample there may be less variation in interparental conflict compared to a high-risk sample. The range of environments present in any given sample has implications for the shape of the cGxE interaction effect that is likely to be observed. We illustrate this in Figure 1. In a low-risk sample, where the range of interparental conflict is somewhat restricted, we would observe a fan-shaped interaction effect, which is consistent with a diathesis–stress model of cGxE. In a high-risk sample, where there is potentially a greater range of
