Interpreting changes in life expectancy during temporary mortality shocks

Abstract

BACKGROUNDLife expectancy is a pure measure of the mortality conditions faced by a population, unaffected by that population's age structure. The numerical value of life expectancy also has an intuitive interpretation, conditional on some assumptions, as the expected age at death of an average newborn. This intuitive interpretation gives life expectancy a broad appeal. Changes in life expectancy are also routinely used to assess mortality trends. Interpreting these changes is not straightforward as the assumptions underpinning the intuitive interpretation of life expectancy are no longer valid. This is particularly problematic during mortality 'shocks,' such as during wars or pandemics, when mortality changes may be sudden, temporary, and contrary to secular trends. OBJECTIVEThis study aims to provide an alternative perspective on what changes in life expectancy measure that remains applicable during mortality shocks. CONCLUSIONSReturning to two different models that the period life table may represent, I show that a difference in life expectancy is typically interpreted from the synthetic cohort model as the difference in mean longevity between different birth cohorts. However, it can also be interpreted from the stationary population model as a measure of premature mortality in a death cohort. The latter, less common interpretation makes more sense for temporary declines in life expectancy induced by mortality shocks. The absolute change in life expectancy is then an age-standardized value of the average lifespan reduction for people dying during the mortality shock. CONTRIBUTIONTo clarify what a decline in life expectancy measures during mortality shocks is important, especially as demographers often assess the mortality impact of those shocks using this metric, which gets widely reported beyond demographers' inner circle.

Lifetime years married held steady for men with a BA degree since 1960 but dropped to lowest level since 1880 for men without a BA

“…Period estimates of expected lifetime years married summarize mortality and marital status conditions in the population in a given year and, like period estimates of life expectancy, are extremely useful as such ( 32 , 33 ). In addition, past research has shown that period life expectancy measures are good estimates of cohort life expectancy, but are lagged.…”

“…However, long-run trends in period measures of life expectancy track those estimated from real cohorts closely, albeit with a lag ( 31 ). In periods of rapidly changing mortality, differences in life expectancy can be interpreted as changes in average years of life lost or gained ( 32 ). Regardless of whether the life expectancy of future cohorts maps onto period estimates, period life expectancy is an extremely useful summary measure of prevailing mortality conditions and trends ( 32 , 33 ).…”

“…In periods of rapidly changing mortality, differences in life expectancy can be interpreted as changes in average years of life lost or gained ( 32 ). Regardless of whether the life expectancy of future cohorts maps onto period estimates, period life expectancy is an extremely useful summary measure of prevailing mortality conditions and trends ( 32 , 33 ). The benefits and limitations of our period estimates of expected lifetime years married are the same as those for life expectancy.…”

Non-survival to pension age in Denmark and Sweden: a sub-national investigation

“…Life expectancy is the best available summary measure of current mortality. Yet, it's quite non-intuitive, or rather the intuitive interpretations of it in terms of individual expected longevity are easily misleading (Aburto et al, 2021;Heuveline, 2023;Luy et al, 2020). Here it's curious how the change of perspective from life expectancy to the probability of dying in the age interval while preserving the spatial pattern almost unchanged sharpens the perception of inequality between the areas -the lagging behind municipalities experience twice higher probabilities of dying compared with the most prosperous municipalities.…”

The effect of the COVID-19 pandemic on life expectancy in the USA: An application of hybrid life expectancy

“…Demographers understand that changes in life expectancy between a prepandemic year and a pandemic year are biased measures of the pandemic’s effect [ 7 , 8 ]. The calculation of life expectancy assumes a group closed to migration and a set of mortality rates.…”