In the absence of prior twin studies of cannabis outcomes in AAs, we can only speculate on the potential sources of this distinction. Considering that the shared environmental influences on cannabis outcomes in EAs overlapped entirely with those that influence maltreatment, it may be that family-level environmental factors that frequently co-occur with maltreatment, such as parental conflict or separation (Bidarra et al., 2016; Hindley et al., 2006) and parental alcohol problems (McLaughlin et al., 2000; Shin et al., 2009), are more closely linked to early and problem use of cannabis in EA than AA girls. This is consistent with findings from our earlier study of sexual abuse and cannabis outcomes, in which the relative contribution of sibling early initiation of cannabis was much greater in EAs than AAs (Sartor et al., 2015).
