Academic journal article Demographic Research

Age Groups and the Measure of Population Aging

Academic journal article Demographic Research

Age Groups and the Measure of Population Aging

Article excerpt

Abstract

BACKGROUND

Measures of population aging are important because they shape our perception of demo- graphic trends. Indicators of aging based on fixed ages contributed to a dramatic portrayal of demographic evolutions, some of which were associated with the myth of decline.

OBJECTIVE

We propose a new measure of population aging, based on the relative age of each indi- vidual in the population. Our approach builds on previous work by Aghevli and Mehran (1981) and relies on optimal grouping techniques that are used to determine the various age groups within a population. The cutoffages for these groups, such as the age from which an individual is considered to be an older person, are then endogenous variables that depend on the entire population age distribution at any given moment.

METHODS

We show how to apply optimal grouping techniques to age distributions and how to calcu- late various indicators of aging, which are invariant with respect to proportional rescaling of distributions. We compute these indicators for the US, and a sample of 13 other indus- trialized countries.

RESULTS

We find that, contrary to common arguments for an aging population, the share of elderly individuals within the total population has not increased much, and has remained stable in these countries. These results complement and reinforce the earlier findings of Sanderson and Scherbov (2005, 2007) who also reassessed the aging phenomenon.

(ProQuest: ... denotes formulae omitted.)

"The first part of life is childhood. The second is your child's childhood. And then the third, old age." Barbara Kingsolver, The Lacuna

1. Introduction

Population aging is often perceived as a very widespread phenomenon. According to the last United Nations "Population Aging Report" (2009), the proportion of the global population aged over 60 years was 8% in 1950, 10% in 2000, and is expected to reach 21% in 2050. In this report, the United Nations have used a very specific, albeit very common, type of measurement for assessing the population aging phenomenon, namely the proportion of population aged over 60. And yet, it is evident that today's 60-year-olds are often very different from their parents at the same age and have absolutely nothing in common with their grandparents at the same age. The age at which one becomes an older person is a notion that changes over time; thus, calculating the proportion of older persons based on a fixed age only provides us with biased information. The use of such an indicator is often justified on the ground that these fixed ages (60, 65 or 80, depending on the study) correspond to the eligibility ages of certain social programs, most notably the pay&endash;as&endash;you&endash;go pension system. However, recent events, for example in Europe, show that these ages also undergo changes (see notably Fenge et al., 2008, and references therein). Indicators, though simple, are not neutral. While studying the history of social representation that defines old age as starting from 60 years, Bourdelais (1994, 1999) showed that indicators of aging based on fixed ages contributed to a dramatic portrayal of demographic evolutions, some of which were associated with the myth of decline. The aim of our paper is to propose a new means of determining the various age groups in a population and to recalculate new indicators of aging based on the cutoffages of these groups.

The main difficulty in characterizing the relative size of older populations lies in the determination of the age at which an individual becomes an older person. We propose to use all the statistical information contained in the population age distribution to define this age. We proceed in the following manner: we predefine a certain number of age groups, then "optimally" divide single age-classes among these different groups. The optimal grouping rule, as proposed by Aghevli and Mehran (1981), consists in selecting cutoffages for groups such that age differences are a minimum within each group and a maximum between groups. …

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