A second main set of analyses analyzed the combined sample of AAs and EAs. In this full sample we included gender, age, population (0=EA, 1=AA), SNP, and SNP*population in the model, and examined the 2 degree of freedom test for significance of the SNP and SNP x population terms together. This approach is sensitive both to SNPs that show consistent effects across populations and also to SNPs that show population-specific effects. This approach is therefore useful for the discovery phase in a diverse sample such as this one. A region harboring SNPs with population-specific effects is of interest, given the differing LD and population histories in EAs and AAs. Such a region can later be fine-mapped or resequenced to determine whether additional underlying genetic variation evidences more similar effects across populations, as would be consistent with a common biological mechanism (Saccone et al., 2008).
