Prospective Old-Age Dependency Ratio

The prospective old-age dependency ratio (POADR) is a measure of population aging that redefines the onset of old age in terms of remaining life expectancy rather than a fixed chronological age such as 65. Proposed by Warren Sanderson and Sergei Scherbov in a 2005 Nature paper, it rests on the insight that what '65' meant decades ago, in terms of years of life and health remaining, is not what it means today as longevity rises. They set a prospective old-age threshold at the age where average remaining life expectancy falls to a chosen value (commonly 15 years), and that threshold rises over time as people live longer. The POADR then counts people above this moving threshold relative to the working-age population below it. Because the threshold advances with longevity, the prospective ratio increases far more slowly — and can even fall — compared with the conventional ratio that fixes old age at 65. Sanderson and Scherbov's provocatively titled finding, that average remaining lifetimes can increase even as populations 'age,' reframed debates about the sustainability of aging societies. The measure is part of their broader characteristics-based approach to age.