Strengths of the present study include the large sample size of African-American subjects, a group that has been under-represented in genetic studies of addiction. Moreover, since the dataset included individuals with polysubstance dependence as well as individuals addicted to a single substance we were able to parse out both specific and general influences of GABRA2 variation on addiction. Furthermore, it should be noted that we corrected for the effects of population stratification by using ethnic factor scores derived from 186 AIMS as covariates in our analyses. The European factor had a significant effect on heroin addiction in most analyses but no effect on cocaine addiction or alcoholism.
