"The use of the new index of years of life lost allows us to relate mortality by age and causes of death to the change of the life expectancy, at birth or between any given ages. This index replaces the use of the multiple decrement life tables for analyzing the impact of the change in mortality by age and cause of death on the life expectancies....The article presents the theoretical derivation of the index, some examples of its use, and a detailed calculation." Examples provided include Mexico, Chile, and Argentina. (SUMMARY IN ENG)