Friday, October 07, 2011

Thinking about HIV statistics.

Wikipedia reports on HIV prevalence in Haiti:
By the end of 2005, the national HIV prevalence among adults aged 15 to 49 was 3.8 percent[2] but has since decreased to 2.2 percent by the end of 2008 due to effective HIV/AIDS education programs, and increased standard of medical treatment.
Lets think about that for a moment. There is no cure for HIV infection; someone infected with HIV remains infected with HIV. So how does the portion of the population infected with HIV go down 42 percent in six years?
  • The population growth rate in Haiti was about 2 percent per year from 2006 to 2009, but went to minus 2 percent in 2010 and was about zero this year. Thus the change in HIV prevalence was not due to an increase in uninfected people without a corresponding increase in infected people.
  • The implication is that the incidence of new cases of HIV infection has gone down, but even if that is true there would have to be some other factor leading to the reduction in the number of infected people.
  • Of course, there could be a preferential migration of HIV infected people to other countries, but it is hard to see why or how that could be.
  • It is possible that something like one and one-half percent of the population infected with HIV died in six years. However, it has been estimated that the death rate from AIDS has gone down significantly.
In fact Index Mundi reports that the prevalence of HIV/AIDS has gone down from six percent of the population in 2001 to two percent in 2007. That would suggest that four percent of the population probably died from the disease in six years. Roughly 40 percent of the Haitian population is under 15 years of age or more than 65, groups which would presumably have low prevalence of HIV infection. Thus the four percent of the total population that presumably died of AIDS related causes represent 6 2/3 percent of the working age population. That is a dreadful tole with important social and economic implications.

Of course, there is the possibility that the estimates of HIV prevalence are not credible. If they were too high in the past or if they are too low now, the trend would be thereby explained. My experience with health statistics in Haiti, some 35 years ago, leads me to distrust any such statistics.


Anonymous said...

I don't know if this post is too late, but for years the UN had exaggerated HIV rates in several countries. This was brought to attention by Indian officials. If you noticed, UN's AIDS commission did not publish data for 2008 when they were forced to revise their data. You'll see dramatic drops in HIV rates for several countries between 2007 and 2009. Haiti's current HIV prevalence rate is lower than that of the Bahamas and Belize.

John Daly said...

Think about the people in Haiti trying to collect and report statistics on HIV, underpaid and overworked in all probability, dealing with a system in crisis. If their statistics are less accurate than those in the United States or Western Europe, it is probably not their fault.

I would note that if you have two estimates of a small fraction, and each of the estimates is likely to be inaccurate, the difference between those estimates is likely to be even more inaccurate.

So don't give up funding AIDS programs because of those reported improvements. said...


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