groups vary in the co-occurrence and comorbidity of these addictive behaviors. However, the temporal order of onset of these comorbidities is not clear, which is important for understanding whether addictive behaviors represent different or similar underlying mechanisms. The authors note that group differences in the co-occurrence and comorbidity of addictive behaviors likely occur when ethnicities have some combination of differential: (1) accessibility, (2) genetic vulnerability, (3) socialization to an addictive behavior, and (4) expectations about the drug or behavioral effects. Studies that examine comorbidity rates and these other factors among ethnicities require large sample sizes in order to disaggregate groups beyond major U.S. racial/ethnic categories. When examining genetic influences, these analyses must also consider the issues of population stratification and genetic admixture.
