A new metric, the “Mean Unfulfilled Lifespan” (MUL), that estimates the impact on lifespan of temporary “shocks” like the COVID-19 pandemic, reduced lifespan by almost nine years in some places at its peak, writes MedicalBrief.
Patrick Heuveline of the University of California presented the MUL in the open-access journal PLOS ONE on Tuesday, finding COVID-19 reduced lifespan by almost nine years in New Jersey at its peak.
The impact of a given cause of death, such as heart attack or car crash, might be illustrated by how much it reduces a metric known as period life expectancy at birth. Period life expectancy at birth is the average number of years that a person born in a certain timeframe would live if death rates from that timeframe remained the same for the rest of his or her life.
However, calculating changes in period life expectancy at birth does not adequately capture temporary shocks to mortality rates—such as those caused by natural disasters or the COVID-19 pandemic.
To better illustrate the impact of temporary disasters on average length of life, Heuveline developed a new metric dubbed mean unfulfilled lifespan (MUL). The MUL is the difference between the average age at death for those who died in a given timeframe, and the average age these individuals would have been expected to reach, if there had not been a temporary shock to mortality rates.
Heuveline then demonstrated the MUL by applying it to data from the ongoing pandemic. In particular, he showed how the MUL could be used to compare the impact of COVID-19 between different regions. For instance, using a rolling seven-day timeframe, his calculations suggest that MUL peaked at 8.91 years in New Jersey and 8.96 years in Mexico City. Considering the entire month of April 2020, MUL may have reached 12.7 years in the Guayas province of Ecuador.
Heuveline notes that uncertainties in MUL may arise from potential differences between reported and actual COVID-19 deaths, and explores how these issues can be accounted for when calculating MUL.
“As a few other demographers, I initially tried to convey the mortality impact of COVID-19 by assessing how much life expectancies would decline during the pandemic,” he said. “When mortality conditions are continuously changing, however, life expectancies are hardly interpretable and I wanted to provide a more intuitive indicator of that mortality impact.”
Study details
The Mean Unfulfilled Lifespan (MUL): A new indicator of the impact of mortality shocks on the individual lifespan, with application to mortality reversals induced by COVID-19
Patrick Heuveline, California Center for Population Research (CCPR), University of California,
Published in PlosOne on 27 July 2021
Abstract
Declines in period life expectancy at birth (PLEB) provide seemingly intuitive indicators of the impact of a cause of death on the individual lifespan. Derived under the assumption that future mortality conditions will remain indefinitely those observed during a reference period, however, their intuitive interpretation becomes problematic when period conditions reflect a temporary mortality “shock”, resulting from a natural disaster or the diffusion of a new epidemic in the population for instance.
Rather than to make assumptions about future mortality, I propose measuring the difference between a period average age at death and the average expected age at death of the same individuals (death cohort): the Mean Unfulfilled Lifespan (MUL). For finegrained tracking of the mortality impact of an epidemic, I also provide an empirical shortcut to MUL estimation for small areas or short periods. For illustration, quarterly MUL values in 2020 are derived from estimates of COVID-19 deaths that might substantially underestimate overall mortality change in affected populations.
These results nonetheless illustrate how MUL tracks the mortality impact of the pandemic in several national and sub-national populations.
Using a seven-day rolling window, the empirical shortcut suggests MUL peaked at 6.43 years in Lombardy, 8.91 years in New Jersey, and 6.24 years in Mexico City for instance. Sensitivity analyses are presented, but in the case of COVID-19, the main uncertainty remains the potential gap between reported COVID-19 deaths and actual increases in the number of deaths induced by the pandemic in some of the most affected countries.
Using actual number of deaths rather than reported COVID-19 deaths may increase seven-day MUL from 6.24 to 8.96 years in Mexico City and from 2.67 to 5.49 years in Lima for instance. In Guayas (Ecuador), MUL is estimated to have reached 12.7 years for the entire month of April 2020.
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