Figure 2 illustrates the mechanisms of G × E interaction on EXT for each environmental moderator. All environmental variables have been coded such that higher values are indicative of greater adversity. For each environmental variable, greater environmental adversity was associated with substantially greater additive genetic variance in EXT, with modest to moderate increases in nonshared environmental variance. Note that the figure depicts the unstandardized variance estimates so that the ACE variance components do not necessarily sum to 1.0. For 3 environmental variables, there was also a modest moderation effect on the shared environmental variance with shared environmental variance tending to be greatest at low levels of environmental adversity. Given the consistency of these results, a plausible hypothesis is that moderation of EXT is due to the overlap among the different environmental variables. To test this hypothesis, we regressed each environmental risk factor on the 1st principal component among the 6 environmental variables, and examined whether the residual variance continued to moderate the ACE effects on EXT. While the common variance across the environmental variables accounted for a large portion of
