The conditional nature of the PTSD diagnosis (i.e. its contingency on exposure to trauma) necessitated the use of a three-level trauma variable when modeling trauma and PTSD in combination. Correct model specification required that more than one category of trauma exposure had the potential to be associated with positive PTSD status. We allowed for this possibility by classifying trauma as assaultive, nonassaultive, and absent rather than simply present or absent. [See Heath et al. (2004) for this approach to structural equation modeling with contingent phenotypes.]
