whether the heritability of cannabis initiation and problems, and their covariance, was modified by the presence or absence of maltreatment (i.e., a putative gene × environment interaction, with maltreatment representing the environmental modifier). Larger sample sizes in the AAs would be required to carefully address this hypothesis. Finally, we collapsed across multiple waves of data. Even though we examine associations with early vs. later initiation, future studies in other samples with systematic longitudinal data, might be particularly informative.
