Individual differences in exposure to childhood maltreatment were attributable to shared (73%) and individual-specific environment, in contrast to some prior studies suggesting the role of genetic influences on exposure to lifetime assaultive trauma in adults (Sartor et al., 2012), but consistent with the idea that a broad index of exposure would be more representative of early familial milieu. While there were no racial/ethnic differences in the contributors to variance in maltreatment, we found evidence of racial/ethnic differences in the factors contributing to cannabis involvement and consequently, in the covariation between maltreatment and cannabis initiation and problems. Specifically, among AAs, we did not find evidence for shared environmental influences on either cannabis initiation or problems, and all covariation with maltreatment was through individual-specific environmental factors, with residual association between stages of cannabis involvement attributable to genetic factors not shared with maltreatment and individual-specific sources partially shared with maltreatment. In contrast, consistent with the prior twin literature on European populations (Verweij et el., 2010), we observed modest shared environmental influences on both cannabis initiation (18%) and problem use (23%) in EAs. Importantly,
