The inclusion of full sibling pairs in the present study allowed us to estimate (co)variation due to the environment shared only by twins. Therefore, these models decompose (co)variance into that which can be accounted for by latent additive genetic factors (A), the shared environment (C), the twin environment (T), and the nonshared environment (E). A homogeneity model which constrains parameter estimates to be equal across genders was compared to a heterogeneity model in which estimates are free to vary across genders, as the family processes in maltreatment and the reporting thereof may differ by gender (Bugental and Shennum 2002; Sunday et al. 2008). Exploratory analyses were also conducted to test whether the pattern of results were similar for the covariation between specific forms of maltreatment (i.e., physical maltreatment and neglect) and conduct problems. We did not examine the covariation between sexual maltreatment and conduct problems because the prevalence of sexual maltreatment was low (i.e., 5.1%).
