Death, demography and the denominator: Age-adjusted Influenza-18 mortality in Ireland

Abstract

Using the Irish experience of the Spanish flu, we demonstrate that pandemic mortality statistics are sensitive to the demographic composition of a country. We build a new demographic database for Ireland's 32 counties with vital statistics on births, ageing, migration and deaths. We then show how age-at-death statistics in 1918 and 1919 should be reinterpreted in light of these data. Our new estimates suggest the very young were most impacted by the flu. New studies of the economic impact of Influenza-18 must better control for demographic factors if they are to yield useful policy-relevant results. Covid-19 mortality statistics must go through a similar procedure so policymakers can better target their public health interventions.

Unequal excess mortality during the Spanish Flu pandemic in the Netherlands

“…The national death registers we relied on included individual information on the age, occupation, and date of death as well as sex and the municipality of residence of the deceased. This information allowed us to estimate the association between social class and excess mortality, while also taking occupational characteristics, age, and regional variation in excess mortality into account ( Colvin and McLaughlin, 2021 , Mamelund, 2011 ). Moreover, controlling for municipality size and presence of local army bases, or analysis of specific regions with high excess mortality resulted in similar estimates of the magnitude of socioeconomic differences in excess mortality during the Spanish flu.…”

“…However, total numbers of deaths from death registration are sometimes deemed the most accurate way to address the impact of an epidemic. Shifts in overall mortality rates do not depend on potentially wrong or missing diagnoses of the cause of death, includes individuals who had multiple diseases at the time of death, and includes indirect deaths from the Spanish Flu ( Colvin and McLaughlin, 2021 ).…”

“…11 Baseline mortality was established by calculating the average mortality of the same occupational groups (by age group) in autumn 1910–1917 (September through December). The Netherlands remained neutral during the First World War, so dramatic changes to the population at risk and mortality rates that characterised many other countries at the time are not expected ( Colvin and McLaughlin, 2021 ). The exception was the year 1914, when the Netherlands briefly took in 1 million Belgian refugees, who largely returned before the end of the calendar year.…”

“…The topic of the Spanish Flu has seen renewed interest by historians and social scientists in recent years ( Boberg-Fazlic et al, 2021 , Colvin and McLaughlin, 2021 , Devos et al, 2022 , Gallardo-Albarrán and de Zwart, 2021 ), though few studies provide in-depth analyses of socioeconomic differences in mortality. Evidence for socioeconomic contrasts in Spanish Flu mortality comes from a number of studies, predominantly at the aggregate level and showing correlations between local conditions and excess mortality.…”