Many countries have social security systems that are currently financially unsustainable. Economists and policy makers have long studied this problem and identified two key causes. First, as declining birth rates raise the share of older persons in the population, the ratio of retirees to...

In nearly every industrialized country, large aging populations and increased life expectancy have placed enormous pressure on social security programs—and, until recently, the pressure has been compounded by a trend toward retirement at an earlier age. With a larger fraction of the population...