As noted in the introduction, it is not possible to distinguish between these two influences in a twin study. Therefore, tests of nonshared environmental influences (E) on maltreatment provide the only true tests of environmental influences on childhood maltreatment, though even this parameter is confounded by measurement error and possible G X E interaction. The effects of children’s genes on maltreatment are clearly child effects, as siblings’ genetic similarity is related to the similarity in their maltreatment experiences. Shared environmental, twin environmental, and nonshared environmental influences may or may not represent child effects. That is, it is possible that these factors capture caregiver behavior that may or may not be in direct response to children’s behavior.
