The Times Online: race based drugs

Yet race is not necessarily a good guide to disease. We all think we know that sickle-cell anaemia is a black disease. Except that it is not. Sickle cell is a disease of populations originating from areas with a high incidence of malaria. Some of these populations are black, some are not. The sickle-cell gene is found in equatorial Africa, parts of southern Europe, southern Turkey, parts of the Middle East and much of central India. Most people, however, only know that African-Americans suffer disproportionately from the trait. And, given popular ideas about race, they automatically assume that what applies to black Americans also applies to all blacks and only to blacks. It is the social imagination, not the biological reality, of race that turns sickle cell into a black disease.

A classic example of making the mistake of taking correlation as causation: you cannot draw the conclusion that sicke cell is a black disease, because of a spurious factor, malaria.