Explanatory Note About UNAIDS/WHO Estimates

The UNAIDS/WHO estimates in this document are based on the most recent available data on the spread of HIV in countries around the world. They are provisional. UNAIDS and WHO, together with experts from national AIDS programmes and research institutions, regularly review and update the estimates as improved knowledge about the epidemic becomes available, while also drawing on advances made in the methods for deriving estimates.

The estimates and data provided in the graphs and tables are given in rounded numbers. However, unrounded numbers were used in the calculation of rates and regional totals, so there may be small discrepancies between the global totals and the sum of the regional figures.

In 2001, new software was developed to model the course of HIV/AIDS around the world and to further enhance the quality of estimates of HIV/AIDS prevalence and impact. As a result, this year's estimates incorporate, in particular, new knowledge and assumptions about survival times for adults and children living with HIV/AIDS. Because of this, some of the new estimates cannot be compared directly with estimates from previous years.

UNAIDS and WHO will continue to work with countries, partner organizations and experts to improve data collection. These efforts will ensure that the best possible estimates are available to assist governments, nongovernmental organizations and others in gauging the status of the epidemic and monitoring the effectiveness of their considerable prevention and care efforts.