For the first time we assess and decompose the trends in lifespan inequality across the world from 1950 to 2015. Using additively decomposable inequality measures, we break down global lifespan inequality in two parts: the within-country and the between-country components – thus allowing a better understanding of the global health dynamics over time. As opposed to other studies focusing on average mortality indicators that disregard within-country variations, our approach allows investigating whether or not the entire age-at-death distributions have been converging or diverging across the globe. Our findings suggest that, as the epidemiologic transition unfolds, longevity increases in tandem with decreases in lifespan inequality. Yet, inspecting the relationship between longevity and adult mortality (i.e. disregarding infant mortality) a different picture arises. While convergence in infant and early childhood mortality has brought steady and universal improvements in life expectancy and lifespan inequality, there are some instances of divergence in adult mortality (e.g. lifespan inequality increases despite further increases in life expectancy).

Lifespan inequality trends are influenced by the compositional change that has taken place during the last decades around the world. On the one hand, population growth has dramatically shifted the population shares distribution over time. On the other hand, impressive longevity gains have typically benefited most countries, but some have benefited more than others have. To gauge the effect that such structural changes have had on lifespan variability across and within countries we have run counterfactual analyses. This technique is helpful to identify the factors that have been more decisive in driving changes in global lifespan inequality. The empirical evidence presented here suggests that the declines in global lifespan inequality have been mainly driven by declines in within-country lifespan variability and, to a lesser extent, by longevity trends across countries. Population growth has played a minor role in this process.