| Summary: | In Sanderson and Scherbov (2005) we introduced a new forward-looking definition of age and argued that its use, along with the traditional backward-looking concept of age, provides a more informative basis upon which to discuss population aging. Age is a measure of how many years a person has already lived. In contrast, our new approach to measuring age is concerned about the future. In this paper, we first explore our new age measure in detail and show, using an analytic formulation, historical data, and forecasts, that it is, in most cases, insensitive to whether it is measured using period or cohort life tables. We, then, show, using new forward-looking definitions of median age and the old age dependency ratio, how combining the traditional age concept and our new one enhances our understanding of population aging.
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