This finding is not necessarily intuitive. For example, each environmental risk factor was significantly correlated with EXT, evidence of a main effect such that mean-levels of EXT increase with greater levels of environmental risk. This has led some to conclude that environmental influence is causative, and that the greater environmental adversity would obscure genetic influences12. Clearly, however, the effect of environmental adversity differs for those who experience it, as many individuals under substantial environmental stress do not exhibit EXT disorders. Therefore, environmental risk factors must also exert differential or moderating effects on the variance of EXT, and it is these moderating effects on the genetic and environmental variance of EXT that provides a model for the mechanisms of environmental risk for EXT psychopathology38.
