The extent to which overlapping genetic and common environmental influences explain the childhood maltreatment–AAD association can be estimated using a modified version of the Cholesky decomposition model (Neale & Cardon, 1992). In this modified Cholesky model, variance in the dependent variable is partitioned into variance overlapping with the independent variable and variance unique to the dependent variable. In the current model (Fig. 2), the first set of factors (A1, C1 and E1) contributes to both childhood maltreatment and AAD. The second set of factors are unique to childhood maltreatment (A2, C2 and E2), and the third set of factors are unique to AAD (A3, C3, E3)1†. Analyses include incomplete pairs as well as subjects with incomplete data using the missing at random (MAR) assumption to account for individuals missing parental psychopathology. All twin models were fit using Mplus™ software version 4.2 (Muthén & Muthén, USA, 2006) using the WLSMV estimation option (for details of twin modeling with Mplus, see Prescott, 2004). We compared a fully saturated model to several reduced models. The goodness of fit of nested alternative models was evaluated using χ2 difference tests (with p<0.05 indicating worse fit).
