Finally, human researchers are provided with two major `experiments of nature' to disentangle genetic and environmental effects: twin and adoption studies. Only rarely are the results of these two methods – which have different strengths and potential limitations – quantitatively compared. For example, in a meta-analytic analysis of the genetics of antisocial behavior, Rhee and Waldman find that heritability estimates are lower in adoption than in twin studies (Rhee & Waldman, 2002). We are fortunate in the field of AUD to have a reasonable number both of high quality twin and high quality adoption studies. Our results show that while heritability estimates are modestly lower for AUD when derived from adoption than from twin studies, the estimates are statistically homogeneous. That is, within the power of the available studies, we obtain the same estimate of the heritability of AUDs from these two main genetic epidemiologic methods. Given the differences in their approach and their distinct potential methodological limitations, we should be considerably more confident in our conclusions about the heritability of AUD given that we obtain similar results from both methods than we could having results from only one of them.
