Even with the limited studies, these findings have implications for genetic research on addictive behaviors. Population stratification is a critical issue in genetics research, which means that smaller racial/ethnic groups are often not assessed in genetic studies that require separation of groups when allele prevalences vary. Careful attention must be paid to differentiating genetic effects within and across ethnic groups. The research indicates not only variation in addiction prevalence and comorbidity across the five major US ethnic/racial categories, but also within ethnic subgroups categorized broadly as Asian, Hispanic, and Native American, and indicates the need to further disaggregate ethnic groups when researching the genetics of addictions. The typically smaller sample sizes for ethnic minority groups result in lower power to detect significant relationships in these groups, but the consistency of effect sizes across ethnic groups can serve as indicators of the stability of the relationships across groups and suggest potentially different etiologies. When effect sizes are consistent across groups, this provides support for the generalizability of the genetic-phenotypic relationships. When effect sizes differ across groups, this suggests the possibility of
