Some limitations of our study need to be considered. First, while the sample is representative of the Minnesota population from which it was drawn, it does not reflect the racial and ethnic diversity of the broader United States population. Also, our sample was limited to late adolescence and so it is unknown whether the same G-E interplay processes are present at other developmental stages. Another limitation is ambiguity regarding the direction of causation. That is, our decision to examine the moderating effects of environmental risk on EXT, although theoretically grounded, is methodologically arbitrary as an argument could be made that EXT moderates the genetic and environmental influences on the environmental risk factors. Supplemental analyses, however, showed that when such effects were present, they were much weaker than the moderation effects on EXT. Future analyses that utilize the prospective design of the MTFS will provide further insight into the causative associations between EXT and these environmental risk factors.
