Can the value choices in DALYs influence global priority-setting?

Abstract

The "disability adjusted life years" (DALYs) are increasingly used as a tool for decision-making and for describing the distribution of the Global Burden of Disease. The "DALY" combines information about mortality and morbidity, with several value choices such as disability weighting, age-weighting and discounting. These value choices imply that life years are assigned different value, depending on the age and the health state they are in. How robust is the distribution of DALYs to changes in these value choices, and are the choices transparent at the point of use? We calculated the burden attributed to "developmental disability due to malnutrition" and "major depression" with alternative value choices in a simple sensitivity analysis. In particular, we explored the relation between disability weight, health state description and incidence rate. The formulae and information needed was found in the World Health Organisation (WHO) publications using DALYs, and in a survey among international health workers. We found that alternative age-weights, disability weights and discount rate led to an inversion in the ranking of the burden of the two conditions. The DALY loss attributed to "developmental disability due to malnutrition" increased from 14 to 90%, while that of "major depression" sunk from 86 to 10%. The value choices currently used, tend at underestimating the disease burden attributed to young populations and to communicable diseases and this goes against the renewed efforts of the WHO of targeting diseases that are typical of poor populations. While the value choices may be changed, lack of transparency is a more profound problem. At the point of use, the number of DALYs attributed to a condition cannot be fully disaggregated. Hence, one cannot know which part of a DALY loss reflects the age group affected, the prevalence, the mortality rates, the disability weight assigned to it, or to how the condition has been defined. A more transparent and useful approach, we believe, would be to present the years lost due to a disease, and the years lived with a disease separately, without disability weights, age-weights and discounting. This would keep the best of the DALY approach and come closer to the aim of disentangling science from advocacy.