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, all of these shared environmental influences overlapped with those related to childhood maltreatment. The residual covariance between cannabis initiation and progression to problems was due to genetic factors that were unrelated to maltreatment. Taken together, these results indicate that the distinctions by race/ethnicity are not in the relative contribution of genes (i.e., heritability) and environment, but rather in the type of environmental influences that contribute to stages of cannabis involvement. While shared environment plays an important role in the association between maltreatment and cannabis outcomes among EAs, only individual-specific factors related maltreatment to cannabis initiation and problems in AAs.
