In recent years, progress has been made in the identification of causative factors in most single gene disorders and those with genes of major effect. In comparison, no genes contributing to a complex disorder have been unambiguously identified. A number of reasons for this have been previously presented in theoretical papers. Alcoholism is such a complex illness and genetic studies into its underlying genetic causes have suffered from lack of power due to small subject numbers, poor selection of control subjects, and over-emphasis on markers with low prior probability of involvement.