The major advantage of the COGA study is its multisite design with similar methods employed at each site, which allowed the investigators to generate very large data sets. One limitation of the study is that by design it focused on families densely affected with alcohol dependence for linkage analysis (although all families of alcoholic probands are included in the prevalence studies). Although such families are ideal for genetic studies, they may not be fully representative of the spectrum of people who suffer from alcoholism, depression, or both. Despite this limitation, the study’s results, in combination with prior studies, suggest that the pattern of disorders in the family is a reasonable clinical characteristic to use for the differentiation of subgroups within alcoholism.
