Figure 1.

Panel A shows the bivariate model that was evaluated. The baseline bivariate model included genetic (A) and non-shared environment (E) latent variables that were common to combat and PTSD (A₁ and E₁) and A and E factors that were specific to PTSD (A₂ and E₂). All paths implicated in the etiology of PTSD were also moderated by combat exposure. Panel B shows the univariate model that was evaluated. This model included regressive paths from combat exposure in both twins to PTSD in twin 1 (the complimentary model for twin 2 is not show in the figure). The model also includes A and E effects for PTSD and moderation of these effects by combat exposure. In both types of models the cross-twin correlation between the A factors was set to 1.0 and .50 for MZ and DZ twins, respectively, and the cross-twin correlation between the E factors was set to 0. M = moderator; sx = symptoms.