Sensitivity of excess mortality due to the COVID-19 pandemic to the choice of the mortality index, method, reference period, and the time unit of the death series

Abstract

Estimating excess mortality is challenging. The metric depends on the expected mortality level, which can differ based on given choices, such as the method and the time series length used to estimate the baseline. However, these choices are often arbitrary, and are not subject to any sensitivity analysis. We bring to light the importance of carefully choosing the inputs and methods used to estimate excess mortality. Drawing on data from 26 countries, we investigate how sensitive excess mortality is to the choice of the mortality index, the number of years included in the reference period, the method, and the time unit of the death series. We employ two mortality indices, three reference periods, two data time units, and four methods for estimating the baseline. We show that excess mortality estimates can vary substantially when these factors are changed, and that the largest variations stem from the choice of the mortality index and the method. We also find that the magnitude of the variation in excess mortality can change markedly within countries, resulting in different cross-country rankings. We conclude that the inputs and method used to estimate excess mortality should be chosen carefully based on the specific research question.

Global and National Declines in Life Expectancy: An End‐of‐2021 Assessment

“…Even in countries with the required good‐quality data, this modeling involves multiple decisions for which there is no clear rule—regarding the number of past years used to define benchmark mortality conditions, if and how a temporal mortality trend is modeled, and so forth—and which may substantially impact the results (Nepomuceno et al. 2021; Schöley 2021). The main challenge to measuring excess deaths with confidence, however, remains substantial data limitations in many parts of the world.…”

Global and National Declines in Life Expectancy: An End-of-2021 Assessment

“…Estimates of declines in life expectancy were derived here from numbers of excess deaths that in turn must be derived from statistical modelling of what the number of deaths might have been in the absence of the pandemic. Even in countries with the required good-quality data, this modelling involves multiple decisions for which there is no clear rule-regarding the number of past years used to define benchmark mortality conditions, if and how a temporal mortality trend is modelled, etc.-and which may substantially impact the results (Nepomuceno et al 2021). The main challenge to measuring excess deaths with confidence, however, remains substantial data limitations in many parts of the world.…”

The Unequal Burden of the Covid-19 Pandemic: Racial/Ethnic Disparities in US Cause-Specific Mortality

“…As noted above in our sensitivity analysis, alternative methods of estimating what mortality would have been in 2020 in the absence of the Covid-19 pandemic would produce different estimates of the effect of the pandemic on mortality. In addition to the choice of modeling strategy, estimates may also be affected by the length of the time horizon used and the granularity of the time unit on the death series (Nepomuceno et al, 2021). In the present study, results were not sensitive to the use of a linear modeling approach based on an extended time series, which may at least partially reflect our use of age standardization to account for changes in the population age structure.…”