When we applied the standard and re-parameterized models to data on interactive effects of child-care quality and genotype (i.e., DRD4) on social skills, we found a significant GXE interaction. The disordinal form of the interaction was confirmed more strongly after fitting the re-parameterized model to the data by showing that both the point and interval estimates of the cross-over point Ĉ were clearly within the range of values observed on the environmental variable. Further, the slope for the high-malleability group (i.e., DRD4-7R) was significant and the slope for the low-malleability group was non-significant, and both of these results proved consistent with tenets of the differential-susceptibility model.
