This same crossover association is also evident in nearly all the top GxE estimates. For example, when the product of the two slopes is calculated for the top 1,000 SNPs sorted in this manner, only six positive values are seen. That is, in 994 of the top 1,000 GWGEI SNPs, we observe opposite associations for the two groups, which is in line with the differential susceptibility model. However, this may simply be an artifact of the number of statistical models that are estimated. To gauge the extent to which this distribution indeed provides evidence for the differential susceptibility model, we randomly assigned each individual to an “environmental status” (with a prevalence equal to the proportion of college graduates in our study) and then estimated a similar GWGEI model. As with the GWGEI-GxE estimates, 987 of the top 1,000 SNPs (sorted by the GxE parameter estimate) evidenced crossovers in which the product of the two slopes was negative. This suggests that these top associations may not necessarily reflect real differential susceptibility in which individuals are responding differently to the environment. Equally
