27 February 2019

New measures show population aging likely to end this century

Policymakers have long been concerned about the effects of an aging population on society, but researchers at IIASA have developed a new tool that shows population aging will likely end by the middle of the century in high-income countries.

© Bumbleedee | Dreamstime

© Bumbleedee | Dreamstime

New measures of population aging will give policymakers a better idea of the policies that could help to deal with population aging in the future, according to IIASA researcher Warren Sanderson and IIASA World Population Deputy Program Director Sergei Scherbov, who cowrote the paper with Patrick Gerland of the United Nations Population Division.

In developed countries, birthrates are falling, while better healthcare and quality of life means that people are living longer than ever. An aging population could present serious problems to societies, if the number of those who can work decreases and the number receiving a pension increases.  It is important to know whether population aging in high-income countries will continue throughout the century or not, because different policies would be more appropriate in one case than another.

If population aging was a transitory phenomenon then policies whose focus was to increase labor force participation rates could be given priority.  This could be done by changing taxes, or by eliminating regulations that reduce pension payments for those who are still working. “Policies like these can reduce decreases in the labor force for a few decades, perhaps, but not in the long-run if population aging persists,” says Sanderson.

If the size of the labor force is expected to continue falling over the remainder of the century, for example, then perhaps policymakers may wish to consider migration policies to dampen the fall. Different policies would need to be designed if population aging were to continue for the entire century or not, it is important to ascertain what the situation will be. 

The new research is designed to provide the background for policy discussions, rather than offer specific policy recommendations.

One difficult aspect faced by the researchers was to define “old”. This is generally taken to be 65 years old and above, known as the ‘conventional’ age, but they note that a 65-year-old in 2000 is unlikely to be the same as 65-year-old in 2100. Ignoring such changes in population characteristics like this can give rise to misleading results. The researchers instead used ‘prospective’ ages, which take changing life expectancy into account, to give a much better indication. Rather than taking a fixed age as being “old”, the prospective age instead defines “old” as having a remaining life expectancy of 15 years. Thus, as life expectancy of a nation rises, so too does the age at which a person can be classed as “old”.

The researchers also looked at the median age of the population, both the conventional and the prospective. The conventional median age divides the population in two, with equal numbers of people above and below that age. The prospective median age standardizes the conventional median age for changes in life expectancy. The researchers used the World Bank definition of high-income countries.  These are the 89 countries in the world with the highest Gross National Income.

The modeling showed that while the proportion of people over the age of 65, the conventional measure for “old”, continues to increase to 2100, the proportion of people with a remaining life expectancy of less than 15 years peaks towards the middle of the century. Similarly, the conventional median age continues to rise through the century, but the prospective median age peaks in around 2040 and then begins to fall.  The peak levels of the prospective proportion of the population categorized as old and the prospective median age are both well below the levels of the conventional measures in the years the prospective measures peak.  The use of prospective ages, a new measure developed at IIASA, and the UN probabilistic population forecasts of age structures, were combined to derive these conclusions.

Sanderson, Scherbov, and Gerland conclude that when the measure of aging used takes into account changing life expectancies, high income countries will not experience continual population aging.  “Policymakers should understand the magnitude of the challenge posed by population aging and the fact that it is temporally limited. This provides them with a much better basis for formulating appropriate policies,” says Sanderson, adding: “Population aging is not a runaway phenomenon.”


Sanderson WC, Scherbov S, Gerland P. (2018) The End of Population Ageing in High-Income Countries. Vienna Yearbook of Population Research 2018

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Last edited: 31 July 2019


Warren Sanderson

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

Sergei Scherbov

Principal Research Scholar and Project Leader Social Cohesion, Health, and Wellbeing Research Group - Population and Just Societies Program

Ansa Heyl

Communications Manager Communications - Communications and External Relations Department

Communications Manager Communications and External Relations Department

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International Institute for Applied Systems Analysis (IIASA)
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