The current HIV/AIDS pandemic is the worst plague ever to afflict humanity, and unfortunately it is at its most severe in southern Africa. Approximately 5 million people are currently infected in South Africa, and therein lies the rub, for our estimates are always based on data that contain uncertainties. While the impact on health is undeniably profound, the uncertainties around the statistics create debate. Our main source of data on the epidemic is the annual report of the Department of Health on HIV prevalence in a sample of pregnant women attending antenatal clinics in the public sector.1 This needs to be extrapolated to the general population, and to do this a series of assumptions (that may differ between different researchers) are needed. Even the population of South Africa is uncertain. While the official population in the 2001 census is 44 819 778,2 this figure is of questionable accuracy. There was an undercount of about 1 in 6 of the population,3 so assumptions and statistical models were required to arrive at the final estimate
