Many analysts have argued that the ageing populations of developing nations represent an economic time bomb for future generations who will have to work to support them. But these fears may not necessarily be justified, according to a study in last week's Nature.
Current estimates of a population's age are based on the average number of years that people have been alive. But more important is the number of years they have left to live, point out Warren Sanderson and Sergei Scherbov. So they have redefined the average age by taking into account how life expectancy will change. The system uses 2000 as a reference year, so if the remaining life expectancy of a 30-year-old in 2000 is 50 years, say, and that of a 40-year-old in 2050 is also 50 years, then the future 40-year-old will have a 'standardized' age of 30.
Using this method throws up some interesting predictions, as populations can effectively become 'younger' through increases in life expectancy, as well as through increased birth rates. Sanderson and Scherbov estimate how the proportion of elderly dependents in a society will change over the twenty-first century for Japan, Germany and the United States - three countries thought to be most at risk from ageing. In fact, the researchers argue, the economic burden of elderly people should begin to decline by the end of the century.
More details: "Average remaining lifetimes can increase as human populations age" Nature 435, 811-813 (9 June 2005)
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