Redefining the meaning of age

Life expectancies and levels of health in many developed and developing countries have increased significantly over the past decades, and are expected to continue increasing. In contrast to these profound changes, the concepts that demographers have used to analyze population-level aging have remained largely static. This project proposes alternative dynamic definitions of age.

© Hans Christiansson | Dreamstime

© Hans Christiansson | Dreamstime

The characteristics approach: Substantial changes in life expectancy and health status in the 21st century have rendered traditional demographic measures of age (defined as time since birth) inadequate for the analysis of aging at the population level. A better understanding of age and aging, for both science and policy, requires new approaches. This project comprehensively reassesses population aging based on innovative alternative definitions and measures that are being developed within the project.

In earlier work, we developed a new paradigm in conceptualizing population aging: the “characteristics approach,” which allows the translation of many characteristics into characteristic-based ages, called alpha-ages [1]. This approach includes chronological age as a special case of alpha-ages and conventional measures of population aging based on these as special cases as well.

However, the characteristics approach is far more general. A number of studies have focused on life table characteristics. Remaining life expectancy has been used for producing a new, forward-looking definition of age, called prospective age. Prospective age has been used to produce new “old-age” thresholds, new proportions of the population who are “old”, new old-age dependency ratios, and new median ages. Short-period mortality rates are a rough but easily measurable health indicator. Alpha-ages based on those mortality rates have been used to assess the proportions of populations who could be considered old from a health prospective [2][3]. World Population Program researchers used the proportion of adult person-years lived after a particular age to construct a simple, hypothetical, demographically indexed, normal-public pension system, which is also intergenerationally equitable. New studies of labor force participation are now incorporating measures of life expectancy and health, and are utilizing the new intergenerationally equitable pension ages [4].

Figure 1. Percentage increase in the proportions of “old” people from 2013 to 2050, using measures unadjusted and adjusted for longevity change, Germany. Note: Prop 65+ is the proportion of the population 65+ years old. It is the conventional measure of the proportion of the population who are old. Prop RLE 15-is the proportion of the population who are in age groups with remaining life expectancy of 15 years or less. It is the prospective measure of the proportion of the population who are “old”. The percentage increases in the proportions “old’ are one measure of the speed of aging. When the prospective measure of the speed of aging is used faster increases in life expectancy lead to slower increases in population aging. Source: [2]


[1] Sanderson WC and Scherbov S (2013). The characteristics approach to the measurement of population aging. Population and Development Review 39(4): 673–685.

[2] Sanderson WC and Scherbov S (2015). Faster increases in human life expectancy could lead to slower population aging. PLoS ONE 10(4): e0121922.

[3] Sanderson WC and Scherbov S (2015). A new perspective on patterns of aging in Europe by education and gender. Journal of Population Ageing, 1–19. doi:10.1007/s12062-015-9125-z

[4] Sanderson WC and Scherbov S (2015). An easily understood and intergenerationally equitable normal pension age. In The Future of Welfare in a Global Europe ed. Marin B pp. 193–220, Ashgate Publishing, Ltd UK.

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Last edited: 29 February 2016


Warren Sanderson

Guest Research Scholar Social Cohesion, Health, and Wellbeing Research Group - Population and Just Societies Program

Sergei Scherbov

Distinguished Emeritus Research Scholar Social Cohesion, Health, and Wellbeing Research Group - Population and Just Societies Program


Forever young?

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