Adoption studies, on the other hand, are based on a comparison of the concordance or correlation between offspring behavior (i.e. drug dependence) and the characteristics of both the biological and adoptive parents: similarity between offspring and biological parents is suggestive of genetic influences on that behavior, while similarity between offspring and adoptive parents is suggestive of environmental influences. Cadoret and colleagues (Cadoret, Troughton, Ogorman, & Heywood, 1986; Cadoret, Yates, Troughton, Woodworth, & Stewart, 1995, 1996) through their adoption studies suggested that genetic and environmental risk mechanisms operate similarly across genders. Their results also highlighted the etiological importance of some environmental influences— particularly parental divorce and parental psychiatric disorders in the adoptive families—in the development of drug abuse. These studies were able to isolate the influence of environmental exposures from potential genetic confounds on risk for drug dependence, thus highlighting the utility of adoption and other family designs for elucidating components of environmental risk. However, adoption studies have certain limitations. Firstly, due to the challenges involved with accessing adoption records, these studies are not common. Secondly, biological parents, adoptive parents and
