While we could not disentangle shared and special twin environmental influences from each other, likely due to low power, there was evidence that broad shared environmental factors were more significant for EA than AA women. This observation aligns well with multiple studies showing that AA youth are less vulnerable to peer effects (Conn and Marks 2014; Mason et al., 2014; Wallace and Muroff 2002) and deviant sibling influences (Catalano et al., 1992) and that, in fact, EA women are most susceptible to peer attitudes towards substance use (Mason et al., 2014). Even though religious attendance is more common in AA youth, its protective association with substance use is more pronounced in EA youth (Wallace and Muroff 2002). As these factors are commonly shared by twin and sibling pairs, we anticipate that they contribute to variance in EA but not AA women.
