The sample used in this analysis comprised 1289 male and 1425 female siblings of probands who participated in the COGA protocol during the first or second phase of data collection, which occurred approximately 5 years apart. The mean age (SD) at the first interview was 36.0 (9.1) and at the second interview was 41.3 (8.8). Fifty-one percent of the sample participated in both phases, 41% in Phase 1 only, and 8% in Phase 2 only. Individuals were coded as positive for an alcohol-related behavior, including DUI arrest, if they reported it in either the Phase 1 or Phase 2 interview, and for a psychiatric or drug use disorder if they met criteria at either interview. Individuals who participated in Phase 2 endorsed more alcohol criteria than those who participated in Phase 1 only. Our analysis was adjusted for this difference in severity as described below in statistical methods.
