New ways to measure age and aging
Defining aging by physical and mental health rather than chronological age makes global population aging look less rapid, research from the IIASA World Population Program shows. It is important to have these characteristic-based measures of age in addition to conventional chronological age, not only because behavior is influenced by expected remaining life expectancy, but because important economic and social aspects depend on it as well.
Most studies of population aging focus on only one characteristic of people: their chronological age. Many other important characteristics, such as physical and mental health, do vary with age, but they also vary over time and from place to place. IIASA research has supplemented traditional measures of aging with new ones that consider characteristics including remaining life expectancy, health, or hand-grip strength.
Many social and economic factors are influenced by these kinds of characteristics. For instance, retired people are already more likely to take courses to help them enjoy new leisure-time activities because they expect to live longer. The number of requests for the provision of certain medical procedures also depends on the number of remaining years of life.
These findings also have consequences for policy. For example, medical expenditures are especially high in the last years of life. In forecasting these expenditures, it is important to take into consideration that, with increasing life expectancies those last years of life happen at an ever older age. Forecasting medical expenditures only on the basis of chronological age produces figures that are too high and could lead to erroneous policy decisions.
Figure 1. Traditional old-age dependency ratio (OADR) (selected Asian countries), 1955-2055.
Pension policy can also be informed by this research. A simple alternative public pension system can also be developed using the concept of α-ages. These correspond to different characteristics of the population and allow us to specify a pension system where the fraction of adult years spent eligible for a pension remains constant. Such a system is equitable in the sense that the ratio of the number of years of pension to the number of years of working remains fixed, even as life expectancy changes. This may help in assessing policies concerning the age at the entitlement to a full public pension.
One of the most commonly used measures of population aging is the change in the “old-age dependency ratio.” This ratio relates the number of “old-age dependents,” who are traditionally assumed to be everyone 65+ years old, to those assumed to support them, people from 20–64. However, rather than assuming everyone over 65 is dependent IIASA researchers use people’s characteristics to define old age, such as a remaining life expectancy of 15 years or less. Figures 1 and 2 show the difference in population aging statistics when using a traditional approach and a prospective, characteristics-based approach. These figures illustrate that predictions for population aging are not nearly as extreme if a characteristics approach is used.
Figure 2: Prospective old-age dependency ratio, based on a remaining life expectancy of 15 years or less (selected Asian countries), 1955-2055.
 Scherbov S and Sanderson W (2016) New Approaches to the Conceptualization and Measurement of Age and Aging. Journal of Aging and Health, 28 (7): 1159-1177.
 Scherbov S & Sanderson WC (2016). New Approaches to the Conceptualization and Measurement of Age and Aging. IIASA Working Paper. IIASA, Laxenburg, Austria: WP-16-005.
Funding: ERC-funded Reassessing Aging from a Population Perspective (Re-Aging) project (under Grant ERC2012-AdG 323947-Re-Ageing).