We examined the fit of an independent pathway model with additive genetic effects and individual specific environment (hereafter AE) (with the seven a priori externalizing disorders and traits assessed in both males and females: ASPD, AAD, DAD, CD, ND, NS and E). The fit of an AE model with separate parameters in males and females (AIC= −209.0) was substantially better than that of a model with shared and individual specific environment (hereafter CE) (AIC= −14.3) or an AE model that forced the parameters to be the same in males and females (AIC= −188.2). Therefore, in the following analyses, we examined AE models separately in MM and FF pairs. In subsequent versions of this model, we substituted the traits N, MD and CaD for E.
