Emily Ostler (a Harvard trained economist doing a post-doc at the University of Chicago) has recently scored big in the publicity department with an article in Esquire entitled, “Three Things You Don’t Know about AIDS in Africa” (see www.esquire.com or to view a video of her presenting this, www.lunchoverip.com/2007/03/ted2007-thinkin.html).  This post is a comment on her reasoning.  She argues that AIDS rates are high in some parts of Africa because not having sex is “like an investment, so you value it more the longer you expect to live.”  That is, people who expect to live longer will take fewer risks of acquiring AIDS by limiting their sexual behavior than people who figure they are going to die soon anyway.   This is especially pertinent in Africa, where the average life expectancy is 40-50 years of age.  Ostler uses data on malaria prevalence and finds exactly that:  people have more sexual partners in areas with alot of malaria than in places with lower risks of death from malaria. 

Here’s the quibble:  Ostler then goes on to point out the we don’t really have very good data on the prevalence of HIV/AIDS in Africa.  She proposes a different measure of prevalence.  She looks at actual death rates in these countries, and then subtracts the estimated death rates without HIV/AIDS.  This gives her an estimate of the number of people who are dying of AIDS, which she then uses as an estimate of HIV/AIDS prevalence.  She says that these estimates “suggest that the HIV rates reported by the UN are about three times too high.”  She may be right.  I hope she is.  But her first point about malaria and sexual behavior works because people are assuming, rationally, that it is not necessary to curtail their sexual behavior because THEY ARE GOING TO DIE OF SOMETHING ELSE BEFORE THE HIV KILLS THEM.  Just because someone dies of malaria does not mean that they did not have HIV.