At first glance, this sounds like good news: those who said they believed that circumcision was effective reduced their risky behaviour – the exact opposite of what one would expect from a Peltzman-type relationship. Wilson et al. chalk this up to a sort-of income effect: now that their baseline risk of contracting HIV is lower (therefore raising potential life expectancy), subjects who have been circumcised decide to invest more in life quality, avoiding dangerous behaviours.
But wait – this nugget of good news is actually obscuring something else: those who didn’t believe that circumcision worked increased risky sexual behaviour – they were less likely to use a condom during intercourse and had more sexual partners. … The increase in risk among the non-believers is disconcerting, even if in net terms there is no increase in risky behaviour. While the believers, who are in the majority, offset the non-believers, we don’t know what the aggregate effects on HIV outside of the sample would be.
Repository of Dish debate on AIDS and MGM here.