A limitation of our study is that we have not performed an analysis of population structure. In other studies conducted in our laboratory (Levran et al. 2008, 2009; Nielsen et al. 2008), 91% of the African-American controls and 95% of the Caucasian controls were analyzed for population structure. Those analyses have demonstrated that the self-identified ethnicities are quite accurate. Furthermore, the Risch group found that self-identification of race/ethnicity of subjects was similar to that found using microsatellite markers and genetic cluster membership; only five of 3,363 subjects were miscategorized (Tang et al. 2005). Similar findings were reported by Liu et al. using 1,334 subjects self-identified as African-American, European American, or Hispanic (Liu et al. 2006).
