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.