provide written consent after the interview allowing use of the data obtained. Data from respondents who either returned consents requesting that their data not be used for analysis (n=17) or did not return their consents (n=10) were neither analyzed nor reported. Study procedures were approved by the ethics committees of the Queensland Institute of Medical Research and the Washington University School of Medicine. Parental data (n=813) are not included from the present study because of concerns that the advanced age of most parents (mean [SD] age: 66.7 [5.7] years) might be a source of bias (eg, secular trends, recall, or censoring). Respondents for whom data were missing for either MDD (n=12) or trauma exposure (n=23) (but not both [n=3]) were included in the analyses. The present study thus focuses on the 1532 twin (996 female, 536 male) and 1059 sibling (625 female, 434 male) respondents for whom trauma, PTSD, and/or MDD data are available. Respondents were almost all white and of European ancestry, but a wide range of educational backgrounds consistent with socioeconomic class diversity was represented in the sample (see eTable 2). Most respondents were married. The mean (SD) age at interview was 37.2 (2.3) years for twins and
