A trivariate genetic Cholesky decomposition was fitted to assess the degree of overlap in genetic and environmental influences between trauma exposure, PTSD and AD. Models were fitted in Mx (Neale et al. 2003) using raw categorical data. Thresholds were adjusted for age at time of report (divided into three approximately equal groups based on age distributions) using two dummy variables for each pheno-type: 13–18 and 22–29, with 19–21 as the comparison group for trauma exposure; 18–19 and 25–29, with 20–24 as the comparison group for PTSD (because all participants were 18 or older when PTSD was assessed); and 13–19 and 23–29, with 20–22 as the comparison group for AD. For those individuals who did not endorse a given condition/diagnosis, age at time of report was coded as age at Wave 4 interview, that is, age at the time the absence of that condition/ diagnosis was reported. A series of submodels examining the statistical significance of A, C and E were compared to the full model to derive the best-fitting trivariate model. Submodels were tested by calculating the difference between the
