Outsurvival as a measure of the inequality of lifespans between two populations

Background Inequality in lifespans between two populations, e.g., males and females or people with low and high socioeconomic status, is a focus of demographic, economic, and sociological research and of public policy analysis. Such inequality is usually measured by differences in life expectancy. Objective We aim to devise a cogent measure of how much distributions of lifespans differ between two populations. Results We propose an outsurvival statistic, φ (phi), that measures the probability that an individual from a population with low life expectancy will live longer than an individual from a population with high life expectancy. This statistic can also be interpreted as an underdog probability – the chance that a random value from a distribution with a low mean will exceed a random value from a distribution with a higher mean. Conclusions Our outsurvival probability complements life-expectancy differences to provide a more nuanced view of the inequality of lifespans between two populations. Our mathematically