Life Expectancy: Frequently Used, but Hardly Understood

Abstract

Period life expectancy is one of the most used summary indicators for the overall health of a population. Its levels and trends direct health policies, and researchers try to identify the determining risk factors to assess and forecast future developments. The use of period life expectancy is often based on the assumption that it directly reflects the mortality conditions of a certain year. Accordingly, the explanation for changes in life expectancy are typically sought in factors that have an immediate impact on current mortality conditions. It is frequently overlooked, however, that this indicator can also be affected by at least three kinds of effects, in particular in the situation of short-term fluctuations: cohort effects, heterogeneity effects, and tempo effects. We demonstrate their possible impact with the example of the almost Europe-wide decrease in life expectancy in 2015, which caused a series of reports about an upsurge of a health crisis, and we show that the consideration of these effects can lead to different conclusions. Therefore, we want to raise an awareness concerning the sensitivity of life expectancy to sudden changes and the menaces a misled interpretation of this indicator can cause.

News from the front: Estimation of excess mortality and life expectancy in the major epicenters of the COVID-19 pandemic in Italy

“…Moving forward, we can gauge how the COVID-19 pandemic would affect annual life expectancy for the year 2020. In the case of anticipated mortality caused by heat waves or cold spells, we typically observe harvesting effect where the frailest population subgroups die while strong individuals survive and later contribute to the number of deaths which are lower than expected (40). In our case, although we do provide a scenario with harvesting effect in the calculation of annual life expectancy for the year 2020, this scenario is unlikely.…”

“…When estimating life expectancy at the end of the year, harvesting (i.e. the reduction in mortality rates following peak mortality associated to shock events) should be taken into consideration (40). Here life expectancy for the entire 2020 is estimated considering two alternative scenarios: 1) conservative scenario; and 2) business-as-usual scenario.…”

The cross-sectional average length of healthy life (HCAL): a measure that summarizes the history of cohort health and mortality

“…Therefore, an observed increase in CAL between two points in time corresponds to the factual longevity gains experienced by individuals present in the given population. By contrast, trends in period LE are more difficult to interpret and might be distorted by several effects such as cohort and tempo effects or heterogeneity [19,32]. For example, the stagnation and rise seen in Danish women's period LE has been attributed to specific cohorts rather than to changes in period mortality conditions [33], and public health researchers are currently investigating to which extent the recent observed stalling in period LE in the UK and Europe represents a "real" deterioration of population health [34].…”

Is austerity responsible for the recent change in mortality trends across high-income nations? A protocol for an observational study

“…The suggestions that this may be due to a natural limit to lifespan being reached is implausible given that: mortality rates have changed across age groups and not just for the oldest; the trends are worst among the poorest groups who already have lower life expectancy; and the countries with the highest life expectancy such as Japan have not experienced a changed trend. More plausible explanations include: cohort effects in the population from historical exposures13–15; influenza, of which there were particularly severe outbreaks in 2015 and 2018; obesity, which has increased across many high-income countries over the last 25 years and is understood to be associated with higher mortality rates16; increased social isolation17 and mental health problems,2 12 18 both of which may be mechanisms linking recession and austerity to mortality. A fuller discussion of the literature on these hypotheses is provided in online supplementary file 1.…”