Quantifying the burden of disease: the technical basis for disability-adjusted life years.

Detailed assumptions used in constructing a new indicator of the burden of disease, the disability-adjusted life year (DALY), are presented. Four key social choices in any indicator of the burden of disease are carefully reviewed. First, the advantages and disadvantages of various methods of calculating the duration of life lost due to a death at each age are discussed. DALYs use a standard expected-life lost based on model life-table West Level 26. Second, the value of time lived at different ages is captured in DALYs using an exponential function which reflects the dependence of the young and the elderly on adults. Third, the time lived with a disability is made comparable with the time lost due to premature mortality by defining six classes of disability severity. Assigned to each class is a severity weight between 0 and 1. Finally, a three percent discount rate is used in the calculation of DALYs. The formula for calculating DALYs based on these assumptions is provided.This paper provides the technical basis for a new measure of the burden of disease, the disability-adjusted life year (DALY). The rationale for measuring such burden, the need for a single indicator, general concepts used in designing such an indicator, a series of specific value choices, and some computational aspects are analyzed. There are four key social choices in any indicator of the burden of disease. First, there are the advantages and disadvantages of various methods of calculating the duration of life lost due to a death at each age. DALYs use a standard expected-life lost based on model life-table West Level 26. Second, the value of time lived at different ages must be considered and is captured in DALYs using an exponential function which reflects the dependence of the young and the elderly on adults. The time lived with a disability is made comparable with the time lost due to premature mortality by defining six classes of disability severity. A severity weight of 0-1 is assigned to each class. Finally, a 3% discount rate is used in calculating DALYs. The formula for calculating DALYs based upon these assumptions is provided.