Sex differences in the magnitude of genetic and environmental influences were examined, as the family processes in maltreatment or the reporting thereof may differ by gender (Bugental & Shennum, 2002; Sunday et al., 2008). First, homogeneity models (figure 1), in which the magnitude of genetic and environmental influences is constrained to be equal across genders, were tested. Second, heterogeneity models, which assume that the same genetic and environmental influences influence both genders but that their effects may differ in magnitude, were tested. Because opposite-sex DZ correlations were not lower than same-sex DZ correlations, models that assume different genetic factors influencing males and females were not considered. To evaluate each of the parameters in the univariate models, reduced models in which each parameter was dropped from the saturated (ACTE) model individually and in conjunction with other parameters were fit.
