Third, the combined genetic variability and family environmental contributions to alcoholism risk in the Iowa CFS and LSS studies total 100 percent, implying that nonshared environmental effects have no impact on alcoholism risk. This result seems implausible. As noted previously, alcoholism in adoptive families could include drinking problems that were caused by the behavior of the adoptee. Thus, the contributions of environmental and genetic variability would not be independent of each other. With the exception of the two outlier studies, in the remaining studies, nonshared environmental influences account for at least 30 percent of the variation in alcoholism risk.
