Life Expectancy Decomposition: The Contribution of Changes in Numerators and Denominators

Wen Su , Australian National University
Vladimir Canudas-Romo, Australian National University

Demographers use ratios, proportions, and rates as the main input of their research, all of which are calculated as counts of numerators divided by denominators. In the case of age-specific death rates, the denominator is the person-years lived in the period of study, and the numerator is the deaths that occur during the period. Period life expectancy summarises those rates into one measure and its changes convey messages of changing mortality between periods, as well as showing progression/deterioration of longevity. In the past, methods have been developed to measure the contributions of different age groups, different subnational groups, and different causes of these changes in period life expectancies. Here we present an alternative perspective that examines the contributions from the two fundamental components to the dynamics of life expectancy changes: the population growth of the person-years in the denominator, and the relative changes in the number of deaths in the numerators. Our results show that population growth at older ages increases life expectancy through the denominator component. At the same time, life expectancy changes varied across populations due to the different age patterns of the numerator component.

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 Presented in Session 48. Life Table Methods and Decompositions in Mortality Research