the Indian population assessed. Given the diversity of Native American populations, our findings may not generalize to other Native Americans. Our study consisted of a cross-sectional sample, which contained individuals who may not have yet passed through the age of risk for developing cannabis dependence and the clinical symptoms used in the cluster analysis. A prospective study would address these limitations. It is important to point out that heritability of a cannabis dependence cluster does not necessarily arise from genetic variation since shared family environments may have contributed to its heritability. Comparisons of linkage findings to non-Indian populations may be limited by differences in a host of potential genetic and environmental variables. The underlying assumption that these phenotypes are normally distributed, an assumption of variance component analyses, may not be warranted. Finally, because this population has significant admixture, estimates of allele frequencies may produce biased LOD scores.
