First, a full bivariate model that estimated all possible unique and common parameters served as the baseline model (model I, Table 3; Fig. 2). In model I, the residual common environmental influence for AAD (C2 loading) was estimated at zero. A reduced model (model II, Table 3) with this parameter fixed to zero had no change in fit (Δχ2=0.0, df=1, p=0.99), and was thus used as the model to which subsequent models were compared. In model II, the maltreatment–AAD overlap was primarily explained by common environmental influences [C1=0.43 (S.E.=0.12)] in addition to the influences of non-shared environment [E1=0.15 (S.E.=0.17)]. There was no evidence for overlapping genetic influences [A1=0.05 (S.E.=1.2)]. Non-shared and common environmental influences account for 0.02 and 0.19, respectively, of the childhood maltreatment–AAD correlation (total ρ=0.21), providing substantial evidence that the childhood maltreatment–AAD association was due primarily to environmental sources shared by twins.
