Refining seasonal mortality estimates through age adjustment: Evidence from Serbia, 2015–2023

BACKGROUNDSeasonal fluctuations in mortality are a persistent demographic and public health phenomenon.The ideal mortality (IDE) framework estimates seasonal excess mortality by comparing observed outcomes with a counterfactual based on the lowest-mortality seasonal window. OBJECTIVESThis study evaluates the validity of the IDE framework when applied to age-and sexspecific mortality in Serbia and proposes an age-structure adjustment (IDEadj) to address anomalies in age-specific estimates. METHODSUsing mortality data for Belgrade and Vojvodina for the period 2015-2023, we construct the IDE baseline based on the three months with the lowest total mortality in each year.Age-specific mortality rates and life expectancy at birth (e) are compared across observed, IDE, and IDEadj scenarios. RESULTSThe IDE framework yields higher life expectancy than observed mortality but produces systematic age-specific inconsistencies.IDE mortality rates occasionally exceed observed values at younger ages and fall to implausibly low levels at older ages, reflecting a mismatch between the age distribution of deaths in the lowest-mortality window and the annual pattern.The IDEadj approach corrects these distortions by aligning agespecific mortality with the observed annual age structure, while preserving the overall magnitude of seasonal gains in life expectancy. CONCLUSIONSAge-structure adjustment improves the internal consistency and interpretability of seasonal mortality estimates without altering their aggregate magnitude.The IDEadj