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Disability adjusted life years (DALYs) have been launched by the World Bank and backed by the World Health Organisation as a measure of the global burden of disease. 1 2 The aim is ambitious: "The burden of disease has yet to entirely replace traditional approaches to the assessment of health needs as an influence on political decision making." 3
Just like quality adjusted life years (QALYs), DALYs combine information about morbidity and mortality in numbers of healthy years lost. In the DALY approach, each state of health is assigned a disability weighting on a scale from zero (perfect health) to one (death) by an expert panel. 2 To calculate the burden of a certain disease, the disability weighting is multiplied by the number of years lived in that health state and is added to the number of years lost due to that disease (figure) Future burdens are discounted at a rate of 3% per year, and the value of the lifetime is weighted so that years of life in childhood and old age are counted less.
Summary points
DALYs (disability adjusted life years) have been launched by the World Bank and the World Health Organisation as a combined measure of morbidity and mortality
The DALY approach explicitly presupposes that the lives of disabled people have less value than those of people without disabilities
The method assumes that disabled people are less entitled to scarce health resources for interventions that would extend their lives
These assumptions are in contrast with basic principles of the WHO
Forced consistency between questions that address different issues produces disability weightings that are basically artefacts; this affects the validity of the global burden of disease report
The ongoing revision of the DALY protocol should address these problems
Though the idea of expressing burden of disease in a single index is tempting, any attempt to summarise information about quality of life and length of life in one number is bound to run into conceptual and methodological problems. The DALY review group of the WHO has criticised DALYs for obscuring too much by pressing complex information into a single numeric measure with a mathematical formulation that "only serves to distract attention from the main issues." 4 Others have raised objections to the way...