In a meta-analysis, we have jointly analyzed data from all studies already mentioned, except the two outliers. Meta-analysis is used to combine data from many different studies to improve the ability to detect small effects by improving the preciseness of estimates. Estimates of genetic and environmental effects did not appear to vary significantly within the group of U.S. studies or the group of Scandinavian studies. In analyzing the U.S. data, estimates for the contributions of the family environment obtained from the adoption data (i.e., based on the Cadoret LSS and CFS samples) and from the twin data were considered separately because of concerns about the measure of the adoptive family’s environmental contribution to alcoholism mentioned previously.
