Compare methods

	Prospective Old-Age Dependency Ratio	Active Life Expectancy Estimation
Field	Social Gerontology	Social Gerontology
Family	Survival analysis	Survival analysis
Year of origin	2005	1983
Originator	Warren C. Sanderson & Sergei Scherbov	Sidney Katz, Laurence G. Branch and colleagues
Type	Demographic ratio using a moving, longevity-based old-age threshold	Life-table estimator partitioning remaining life into active and dependent years
Seminal source	Sanderson, W. C., & Scherbov, S. (2005). Average remaining lifetimes can increase as human populations age. Nature, 435(7043), 811-813.	Katz, S., Branch, L. G., Branson, M. H., Papsidero, J. A., Beck, J. C., & Greer, D. S. (1983). Active life expectancy. New England Journal of Medicine, 309(20), 1218-1224.
Aliases	POADR, Prospective Dependency Ratio, Sanderson-Scherbov Dependency Ratio, Remaining-Life-Expectancy Old-Age Ratio	ALE, Disability-Free Years Expectancy, Independent Life Expectancy, Active vs Dependent Life Years
Related	3	4
Summary	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.	Active life expectancy (ALE) estimates how many of an older person's remaining years are expected to be lived in an active, independent state — free of disability in basic activities of daily living — as opposed to a dependent state requiring help. Introduced by Sidney Katz, Laurence Branch, and colleagues in 1983 in the New England Journal of Medicine, it answered a question that ordinary life expectancy cannot: not just how long people live, but how much of that life is lived in good functional health. The method combines age-specific mortality with the prevalence or transitions of ADL disability within a life-table framework, partitioning total remaining life into active and dependent components that sum to overall life expectancy. Katz and colleagues showed, using data from older adults in Massachusetts, that active life expectancy declines faster than total life expectancy with age and differs across groups. The concept reframed the goal of aging policy from merely extending lifespan to extending the active, independent portion of it. It launched the broader field of health expectancy measures and remains foundational to studying the compression or expansion of late-life morbidity.