Sunday, July 10, 2011

Mathematical Modelers: the Latter-Day Myth Makers

Although I'm not that comfortable with mathematical models, even I know that if you use obscene values you will get obscene results. So the model used by UNAIDS to persuade people that Africans have inordinate and unfeasible levels of unsafe sex is an interesting case in point.

Scratch the surface a little and you'll wonder whether UNAIDS is manned by robots, idiots or fascists (or perhaps all three are compatible). Almost everyone in the example population faces some kind of risk from HIV. And almost everyone is at relatively high risk of being infected sexually, even though sexual transmission is not very likely for the majority of people anywhere.

The most obscene figures, to my mind, are the ones for transmission through medical injections and blood transfusions. However you could argue that the most obscene figures are the ones that are not included at all, those for transmission through other healthcare risks, perhaps risks associated with traditional practices and with cosmetic practices, such as tattooing, hairdressing, manicure and pedicure.

Eva Deuchert and Stuart Brody published an article on mathematical models entitled 'Plausible and Implausible Parameters for Mathematical Modeling of Nominal Heterosexual HIV Transmission' in 2007. They warn that not all transmission is through heterosexual sex and that not all heterosexual sex is penile-vaginal; some is anal, which carries a much higher transmission risk.

The authors also mention the possibility that mathematical models can be intimidating to many readers, who may conclude that it's all so complicated that it must be true. But it is vital for anyone trying to understand how UNAIDS come up with such strange conclusions to spend a bit of time with the models. It is important to criticize the policies they so frequently claim resulted in reductions in HIV transmission and that these reductions were a direct effect of sexual behavior change.

Firstly, sexual behavior was not (or not wholly) responsible for the massive HIV epidemics experienced by a number of sub-Saharan African countries. And therefore, changes in sexual behavior could not have resulted in drops in prevalence. But secondly, far higher levels of 'unsafe' sexual behavior than have ever been identified (and probably higher than is possible for humans) would not result in the rates of HIV transmission found in the worst hit countries.

UNAIDS and others who believe their unwarranted assumptions about sexual transmission in (some parts of) Africa then need to impute all sorts of things to Africans in order to explain serious epidemics. They need to ignore any non-sexual risks and even the elevated risk from anal sex. And this means that, even if people wanted to avoid various risks, they wouldn't even know that what they were involved in was risky.

The authors also put their finger on an important reason why it only seems like sex workers face very high risks as a result of their sexual behavior: if they do have any symptoms that seem like sexually transmitted infections, they could face the higher risk of being 'treated' with unsafe infections. UNAIDS have never even acknowledge the mystery behind extremely high HIV rates among sex workers. It’s a mystery because HIV prevalence among sex workers in most countries is very low.

Similar remarks apply to truckers and all the other people who are said to be at high risk of HIV infection. If they are really as sexually active as they are said to be, they will probably be infected with a sexually transmitted infection, eventually. And then they face the even considerable risks that go with unsafe treatment. The rounding up of sex workers, truckers and other ‘risk groups’, especially in the 80s and 90s, may well have done as much to spread HIV as it did to persuade donors that their money was being well spent.

The public is so used to hearing about these strange Africans with their bizarre sexual behaviour, they don't even notice that they are being asked to believe that significant numbers of people have up to 47 sexual contacts per day, that 20% of unmarried women have 25 sexual contacts per month and that 2% of married women have 100 sexual contacts per month.

This crazy mathematical model that UNAIDS put so much faith in, along with a whole lot of other similarly crazy models, has very serious consequences. They are used to support HIV policies which achieve little but the reinforcement of stigmatizing attitudes. Those policies have not resulted in reducing HIV transmission and they never will. We need to look beyond the pompous tones, the pretty pictures and graphs and the impressive looking models and see UNAIDS policy documents for what they are: dangerous lies.


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