The dependent variable was indexed by the assignment of subjects who met DSM-IV (American Psychiatric Association 1994) criteria for lifetime alcohol dependence. This was assessed using a diagnostic algorithm based on responses to the Semi-Structured Assessment for the Genetics of Alcoholism-II (Hesselbrock et al. 1999; Nurnberger et al. 2004). This outcome was chosen because this was the phenotype originally associated with GABRA2 in early COGA publications (Edenberg et al. 2004). Alcohol dependence was coded 1 if the respondent was classified as dependent according to these criteria, else 0. Thirty-six percent of the analysis sample met DSM-IV criteria for alcohol dependence.
