A limitation of the Copenhagen study is that no direct interviews were conducted with adoptive parents; therefore, the possibility that selective placement occurred, leading to an above-average probability that the child of an alcoholic biological parent would be raised by an alcoholic adoptive parent, cannot be completely ruled out. Such selective placement would cause the importance of genetic effects to be overestimated. It seems implausible, however, that this effect could completely explain the elevated risk to adopted-away sons of alcoholic parents, since their risk is no less than that to nonadopted sons of alcoholics. Family history reports by the adoptees suggest that, if anything, alcohol problems were less prevalent in the adoptive fathers of the adoptees who were sons of alcoholics (12 percent) than in the control adoptees (22 percent), a result which also suggests that selective placement of adoptees could not explain these findings.
