Significant G × E is present when controlling for the main effects of passive rGE (maternal ASP symptoms), MAOA genotype and exposure to childhood adversity (Table 4). The significant effect of MAOA on risk for CD reflects the effect of the low/low genotype across low levels of exposure to childhood adversity. The direction of the interaction effect represents the increased risk associated with the high/high and heterozygous genotypes in the presence of higher levels of childhood adversity. The detection of this interaction occurs where the distribution of exposure to childhood adversity is the greatest, highlighting that the ability to detect this interaction is derived from the extremes of the distribution. However, very few cases reside at the highest levels of exposure (Table 5), indicating low power to detect significant G × E using this model. In an attempt to address this issue, a modified ridit transformation (Bross, 1958) was performed to adjust the measure of environmental exposure by the sample size at each level of childhood adversity. The modified ridit transformation determines a score for each category, which is defined
