Even excluding individuals with no African ancestry, which are probably the result of survey errors, we still estimate a higher European, and corresponding lower African, mean genetic ancestry proportion in 23andMe African Americans compared to previous studies of African Americans. A significant difference between the 23andMe cohort of African Americans and many groups previously studied is geographic sampling. Our cohort reflects heavier sampling of individuals living in or born in California and New York, probably driven by population density as well as awareness of genetic testing or 23andMe. Both are regions where African Americans have lower mean African ancestry than other studies of African Americans, which are often drawn from locations in the South. However, participation in 23andMe is not free and requires online access, so therefore it is important to note that other social, cultural, or economic factors might interact to affect ancestry proportions of those individuals who choose to participate in 23andMe.