Race and continent of origin
I'v posted several times before about the use of race in medicine, specifically the case of BiDil, which may or may not work better in blacks than whites. One concern I and others have had is if self-reported race accurately reflects actual genetic background. The answer to that question seems to be yes, at least in Cleveland:
According to a letter (full text only for subscribers) in a recent NEJM, whites have DNA that is almost entirely of European origin, whereas blacks have DNA that is an admixture, but with a majority of African origin (more accurately of recent African origin, as all human DNA is of African origin if you go back far enough).
This matters because if you believe that self-reported race may be useful in medicine, as I tentatively do, it is because race is a marker for genetic differences. As micro-array technology (DNA chips) progress we'll bypass the need for race and look at genetic differences directly, but until that is possible race may at times be a useful marker.