Catching Up on Mortality, Falling Behind on Disability: A Dynamic Decomposition of the Health‑Adjusted Life Expectancy Gap between Higher‑Income and Lower‑Income Countries

Background: Global health inequalities are conventionally assessed through the mortality gap, yet the joint contribution of mortality and disability to health‑adjusted life expectancy (HALE) gap and their dynamic evolution remain poorly understood. We aim to decompose the HALE gap between higher‑income and lower‑income countries into mortality and disability drivers, separate long‑term trends from transient fluctuations, and reveal heterogeneity within the low‑income group.

Methods: Using data from the Global Burden of Disease Study for 199 countries (122 higher‑income and 77 lower‑income) from 2010 to 2019, we decomposed the HALE gap by age and cause via Horiuchi’s method. Empirical mode decomposition separated each contribution time series into a long‑term trend and residual fluctuations, enabling classification into dynamic archetypes: mortality catch‑up, mortality divergence, disability catch‑up, or disability divergence. Principal component analysis and partitioning around medoids clustering explored heterogeneity among lower‑income countries, and generalized additive models assessed variation along the Socio‑demographic Index (SDI) gradient.

Results: The HALE gap narrowed from 9.10 to 7.93 years, with mortality contributing 6.87 years and disability 1.06 years in 2019. Mortality catch‑up was concentrated in childhood infections and maternal conditions, while mortality divergence occurred for non‑communicable diseases in adults. Disability divergence was driven by mental, musculoskeletal, and sense organ disorders. Low‑income countries clustered into a high‑mortality group (mainly sub‑Saharan Africa and South Asia) and a disability‑emerging group (Asia, Latin America). Along the development gradient, disability progressively dominated the HALE gap.

Conclusions: The converging HALE gap masks a diverging disability gap. Sustainable progress in global health requires explicitly targeting the growing burden of non‑fatal conditions alongside persistent mortality inequalities. The dynamic framework introduced here offers a reusable monitoring tool for health inequality.