DALYs: the age-weights on balance

In studies for the 1993 World development report: investing in health Murray et al. developed the disability-adjusted life year (DALY). This article examines one particular aspect of the DALY methodology: the weighting of life years by age. For the quantitative implementation of this notion Murray proposed a general equation to weight life years by age, which specifies that the years lived between the ages of 9 and 54 years have a weight greater than unity, and for the years outside this range less than unity. The age-weighted life years are used to calculate the "expected years of life lost" (EYLL). Comparison of age-weighted and unweighted age-specific life expectancies shows that the age range which becomes more important due to weighting is not 9-54 years, but 0-27 years. This happens because the EYLL is an age-weighting system in itself, emphasizing the young. The result of piling one age-weighting system on top of the other gives an even stronger emphasis on the young than the EYLL generates by itself. Although this is unlikely to upset the results from the Global Burden of Disease study, we do not think it is desirable. And it is certainly different from what we were led to expect.