Uncertainty in estimates of HIV/AIDS: the estimation and application of plausibility bounds

Abstract

Objectives: To establish the accuracy of the country specific estimates of HIV prevalence, incidence, and AIDS mortality published every 2 years by UNAIDS and WHO. Methods: We review sources of error in the data used to generate national HIV/AIDS and where possible estimate their statistical properties. We use numerical and approximate analytic methods to estimate the combined impact of these errors on HIV/AIDS estimates. Heuristic rules are then derived to produce plausible bounds about these estimates for countries with different types of epidemic and different qualities of surveillance system. Results: Although 95% confidence intervals (CIs) can be estimated for some sources of error, the sizes of other sources of error must be based on expert judgment. We therefore produce plausible bounds about HIV/AIDS estimates rather than statistical CIs. The magnitude of these bounds depends on the stage of the epidemic and the quality and coverage of the sentinel HIV surveillance system. The bounds for adult estimates are narrower than those for children, and those for prevalence are narrower than those for new infections.Conclusions: This paper presents a first attempt at a rigorous description of the errors associated with estimation of global statistics of an infectious disease. The proposed methods work well in countries with generalised epidemics (.1% adult HIV prevalence) where the quality of surveillance is good. Although methods have also been derived for countries with low level or concentrated epidemics, more data on the biases in the estimation process are required.

A global analysis of trends in the quality of HIV sero-surveillance

“…In addition, the end of 2003 estimates have used the present analysis of the quality of HIV serosurveillance for the construction of ranges of certainty around the estimates of people living with HIV/AIDS, new HIV infections, and AIDS mortality, 14 as described in the accompanying paper. 15 The current analysis presents a number of limitations. Firstly, while efforts were made to include all available information, it is inevitable that for some countries the information used may have been incomplete, resulting in a lower score.…”

Monitoring scale-up of antiretroviral therapy programmes

“…11 Countries are strongly involved in the estimation process, which is accompanied by regular consultation between countries and WHO and UNAIDS, and a biannual global effort to train country staff in the estimation methods and software.…”

“…Uncertainty ranges around the estimates have also been provided. 11 WHO recommends that in resource-poor settings, adults and adolescents with HIV should start ART when the infection has been confirmed and there are clinical signs of advanced disease (HIV disease stage IV, irrespective of CD4 cell count; stage III with CD4 cell count less than 350 cells per µl) or laboratory evidence of severe immuno-suppression (CD4 cell count less than 200 per µl or, if not available, lymphocyte count less than 1200 µl with symptomatic disease). 12 There is little direct evidence about the time from seroconversion to clinical AIDS or any of the above treatment eligibility criteria.…”

Maximising the global use of HIV surveillance data through the development and sharing of analytical tools

“…The quality of sero-surveillance in each country has been used to help construct plausibility bounds around the UNAIDS/WHO end-2003 HIV/AIDS estimates generated by the above tools. 23 As explained in the first three papers in this issue, different information sources and different assumptions are used to create national estimates. The accuracy of these estimates depends critically on the quantity and quality of HIV prevalence data, as well as the assumptions used to translate these data into national estimates of the number of adults living with HIV/ AIDS, new infections and deaths among adults, and the number of children newly infected with HIV, living with HIV/AIDS, and child deaths.…”