Researchers at the University of Washington and the United Nations have found that by the year 2100, the global gap between seniors over the age of 85 and workers will grow dramatically more distant than expected in what they called “a worldwide phenomenon.”
The research suggests that there will be fewer working-age adults to support these (presumed retired) seniors than previously expected, which could lead to decreases in support for social security programs for elderly adults.
In China, the world's most-populous country, the number of working-age adults for each person 65 or older will shrink from 7.9 in 2010 to 1.6 in 2100. The ratio in India, the world's second-most-populous country, will decrease from 11.1 in 2010 to 2.0 in 2100.
The model indicates that the United States' ratio would decline from 4.6 in 2010 to 1.8 by the end of the century. Other developed nations with low fertility rates show somewhat larger declines, including the Netherlands dropping from 4.0 to 1.6 and the United Kingdom dropping from 3.6 to 1.6 by century's end.
"The United States has more favorable numbers than other developed countries now, and will retain a slight advantage over other countries at the end of the century," said lead author Adrian Raftery, UW professor of statistics and sociology. He attributed the United States' relatively promising outlook to the country's higher levels of new births and to immigration.
Raftery and his co-authors developed a Bayesian statistical approach that produces a low and high estimate for each country's population as well as the likelihood that the actual population will fall in that range. The method makes population predictions based on countries' previous fertility and mortality rates and immigration patterns.
"We don't know for sure what will happen in the future, but this model gives us a better sense of the accuracy of the projections," Raftery said.
Raftery hopes to use this model to help the United Nations make its 2012 prediction of world population growth, which will be released in February 2013. Previously, he used a similar statistical model with the United Nations' 2010 population prediction. That model projected a world population of 10.1 billion by 2100, which is 1 billion more than previously thought.
The study was published Aug. 20 in the online edition of the Proceedings of the National Academy of Sciences.