How to measure the burden of mortality?
OBJECTIVES: To explore various methods to quantify the burden of mortality, with a special interest for the more recent method at the core of calculations of disability adjusted life years (DALY). DESIGN: Various methods calculating the age schedule at death are applied to two historical life table populations. One method calculates the "years of life lost", by multiplying the numbers of deaths at age x by the residual life expectancy. This residual life expectancy may be discounted and age weighted. The other method calculates the "potential years of life lost" by multiplying the numbers of deaths at age x by the years missing to reach a defined threshold (65 years or 75 years). METHODS: The period life tables describing the mortality of Dutch male populations from 1900-10 (high mortality) and from 1990-1994 (low mortality). RESULTS: A standard life table with idealised long life expectancy increases the burden of death more if mortality is lower. People at old age, more prevalent if mortality is low, lose more life years in an idealised life table. The discounted life table decreases the burden of death strongly if mortality is high: the life lost by a person dying at a young age is discounted. Age weighting the discounted life table balances the effect of discounting. CONCLUSIONS: For the purpose of description of the burden of mortality, the aggregate life table of the studied populations gives the better description of the age schedule at death. Discounting and the use of idealised lifetables as a standard increase the burden of mortality of degenerative disease at the end of life. The age weighted discounted life table violates the principle of parsimony.