Steady state assumptions in DALYs: effect on estimates of HIV impact

Objective-The disability adjusted life year (DALY) and the healthy life yea r (HeaLY) are both composite indicators of disease burden in a population, which combine healthy life lost from mortality and morbidity. The two formu lations deal with the onset and course of a disease differently. The purpos e of this paper is to compare the DALY and HeaLY formulations as to differe nces in apparent impact when a disease is not in an epidemiological steady state and to explore the implications of the differing results. Design-HIV is used as a case study of a major disease that is entering its explosive growth phase in large areas of Asia. Data from the global burden of disease study of the World Bank and World Health Organisation for 1990 h as been used to compare burden of disease measures in the two formulations. Setting-The data pertain to global and regional estimates of HIV impact. Re sults-The DALY attributes life lost from premature mortality to the year of death, while the HeaLY to the year of disease onset. This results in very large differences in estimates of healthy life lost based upon the DALY con struct as compared with the HeaLY, for diseases such as HIV or those with a strong secular trend. Conclusion-The demonstration of the dramatic difference between the two ind icators of disease burden reflects a limitation of the DALY. This informati on may directly influence decision making based on such methods and is crit ical to understand.