A potential limitation of not statistically controlling for environmental effects is that many COA studies included in the meta-analysis ascertained their samples based on one of the parents having the disorder of interest. As described above, these disorders are more common in AD individuals and are heritable traits. Thus, we would expect a bias of increased rates of these disorders in the COA domain. This might account for the effect size of ODD in the COA literature being higher than in the PAE literature. However, this was not true for studies reporting on ADHD or CD. In addition, although the home environment may be more detrimental in one domain compared to the other, the finding that overall rates of ADHD were higher in PAE, whereas ODD rates were higher in COA indicate that the home environment is not preferentially accounting for effects in one group compared to the other.
