Stagnation or Measurement Artefact? Re-Evaluating the Recent Mortality Slowdown in Selected Low Mortality Countries

Tamara Vaz , Vienna Institute of Demography
Magdalena Muszynska-Spielauer, Vienna Institute of Demography, Austrian Academy of Sciences
Marc Luy, Vienna Institute of Demography

During the 2010-2019 decade, many high-income countries (such as the USA, UK, Canada) experienced a notable slowdown or stagnation in life expectancy at birth (e0) gains. Although public health factors are often cited, this paper questions whether this trend is a complete demographic reality or a measurement artefact. Life expectancy (e0), as an aggregative index, inherently becomes less sensitive to mortality improvements at older ages when the mortality improvements shift to older ages, potentially masking continuous progress. The central innovation of this work is the application of the Segmented Interpretable Lee-Carter (SI-LC) model. This method overcomes the limitations of e0 by modeling the entire age-period mortality surface, identifying structural breaks via dynamic programming, and generating a longevity index that equally weights proportional changes in mortality across all ages. Preliminary results (USA, UK, Canada, Japan) demonstrate that the SI-LC index reveals very different dynamics than those captured by e0. Notably, for UK males, while e0 suggests modest and stabilizing gains, the SI-LC index shows a significant acceleration in mortality improvements (from 0.88% to 2.08% per year in the 1999-2019 period), indicating strong gains at older ages. In Japan, e0 shows a constant slowdown, but the SI-LC detects alternating periods of acceleration and deceleration, including a recent re-acceleration (2.56% in 2010-2018). In the US, the index captures a more pronounced deterioration than e0. We conclude that the "stagnation" narrative is incomplete and that the SI-LC provides a more accurate assessment of complex mortality patterns.

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 Presented in Session 27. Mortality and Longevity