as the first term in the model to enable its sharing of additive genetic variance with trauma exposure and PTSD to be easily calculated. The sample’s complex family structure (ie, containing variable numbers of same-sex and opposite-sex twins and siblings), coupled with the presence of fewer comparisons informative for calculating parameter estimates for PTSD (due to coding individuals not exposed to trauma as missing), limited the ability to calculate separate parameter estimates for women and men. We instead controlled for possible sex differences by including sex as a covariate in all the models. Models were fitted to raw data, allowing for maximal use of data and providing −2 times the log-likelihood as an index of fit. After the saturated model was tested, paths with very small loadings (<0.10) were removed. The difference between the log-likelihood of the saturated and reduced models can be interpreted as a χ2 with the degrees of freedom equal to the difference in the number of parameters estimated. Paths that were not significant were dropped from the model. The significance of paths with larger loadings was confirmed with calculation of CIs. A saturated trivariate Cholesky (ie, MDD, low-risk trauma, and high-risk trauma) was created for supplementary
