China: About 1 billion people are of working age, and 74 percent of all adults are active in the labor force. The potential labor force has doubled in size since the early 1970s but will decline in the future due to a rapid fall in the fertility rate from nearly three children per woman in 1980 to 1.6 children today. Even if fertility rates increase slightly, China's economy will be powered by a potential labor force that is nearly 20 percent smaller by 2050.

India: The world's second largest country will surpass China as the world's largest population in about 10 years, with a fertility rate of more than 2.5 children per woman, although fertility rates are falling. Some 800 million people, 64 percent of the population, are of working age, a number that is likely to increase and may push economic growth. India's labor force participation rate is low at 58 percent, however, due to the fact that just one-third of women work outside the home.

United States: If U.S. fertility rates stay at replacement level, the potential labor force is projected to grow slightly. The fact that the country is home to the highest number of international migrants in the world also has an impact on this development. Similar patterns of change in the labor force can be observed in other industrialized countries.

Uganda: With over six children per woman, Uganda has one of the world's highest fertility rates, and nearly half of the population is younger than 15. If these numbers remain high, as they have for decades, the country will need to generate more than 1.5 million new jobs annually by the late 2030s. In 2009, only some 100,000 new jobs were created in Uganda.

Faced with these projections, many policymakers in industrialized countries have expressed alarm about healthcare and pension system costs for an aging workforce. But policies that promote an extension of working years for healthy and productive older adults may help offset the economic consequences of demographic change.