We assessed the impact of ancestrally poorly-matched public controls on power by simulating two genetically-admixed populations (our study population and the public control population). We assumed our study population consisted of individuals derived from two ancestral populations (POP1 and POP2), with subjects having a mean proportion of POP1 equal to 0.25 and standard deviation equal to 0.15. Furthermore, we assumed that study cases had a mean proportion of POP1 ancestry equal to 0.221 and study controls had a mean proportion of POP1 ancestry equal to 0.253. These values are consistent with the estimated proportion of European ancestry in African American prostate cancer cases and controls (Haiman et al., 2007). For public controls, we allowed the mean proportion of POP1 ancestry to vary between 0.10 and 0.40 and assumed a fixed standard deviation of 0.15. We maintained the overall frequency of the susceptibility allele to be fD = 0.30 in the study population, but varied fD between 0.00 and 0.60 in POP1 (in both the study and public control populations). Finally, we assumed that any extreme outliers, such as individuals with
