Participants came from the Collaborative Study on the Genetics of Alcoholism (COGA; Begleiter et al., 1995), a multi-site study that was designed to identify genes involved in alcohol dependence and related phenotypes. Probands were identified through alcohol treatment programs at six U.S. sites and were invited to participate if they had a sufficiently large family (usually sibships of more than three with parents available) with two or more members in the COGA catchment areas. Population-based comparison families were also recruited. Data collection for COGA started in 1991 when adults in the target extended families were invited to complete the Semi-Structured Assessment for the Genetics of Alcoholism (SSAGA), a comprehensive interview that assesses alcohol use disorders and other psychiatric phenotypes such as major depressive disorder and conduct disorder (Bucholz et al., 1994). Approximately 5 years later, adults in the COGA extended families were invited again to complete a SSAGA interview (regardless of whether they completed interviews in the first wave); thus some adults had one interview while others completed two SSAGA interviews.
