Active Life Expectancy Estimation
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.
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