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January 2004, Vol. 10, No. 1 Aging Estimates of current life expectancy at birth are routinely provided by national and international statistical agencies. These figures are important to policymakers because they measure progress in lowering a country’s overall level of mortality. Expected future trends are crucial to government officials, who project public health care and pension expenditures. The United Nations Population Division publishes estimates of life expectancy for all countries in the world, ranging from a low of 37 years in Sierra Leone to a high of 80 years in Japan for the period 1995–2000. In the United States, estimates are 74 years for men and 79 years for women in 1997. These numbers, based on one of the oldest and most fundamental tools of demography, may be overestimated by up to a few years in contemporary countries with high life expectancy, say two demographers who have analyzed past and projected trends in mortality. In a paper published in the Proceedings of the National Academy of Sciences, John Bongaarts and Griffith Feeney question the accuracy of the underlying calculations that generate life expectancy figures. Bongaarts, vice president and director of the Population Council’s Policy Research Division, and Feeney, an independent consultant, identify a distortion in the calculations and provide a formula to amend the figures. The distortion, which Bongaarts and Feeney term the “tempo effect,” has long been recognized by demographers studying fertility; the authors are the first to apply the calculations to mortality. In the case of fertility, tempo refers to the timing of childbirth: when women delay childbearing to later in life, fewer births occur in a particular year. Conversely, when women have children at a younger age, the number of births in a particular year will be inflated. The postwar “baby boom” in the United States, for example, was due in part to a decline in the average age at childbearing during the late 1940s and 1950s. Similarly, the low fertility observed throughout much of the 1970s and 1980s in the United States, western Europe, and Japan was in part due to an increasing age at childbearing, rather than an actual decrease in births per woman, the authors say. According to Bongaarts and Feeney, the tempo effect influences mortality rates in much the same way. The medical advances currently experienced by developed countries raise the average age of death, whereas a deadly epidemic like AIDS can lower the age. We don’t live quite as long While a reduction of two or three years may not seem like a big difference on the individual level, the societal implications are considerable. “We don’t live quite as long as we thought we did,” Bongaarts says. “And in the long run, two or three years can have a substantial impact on the total future expenditures on pensions and health care for the elderly.” Furthermore, the differences between countries are quite substantial and somewhat surprising, Bongaarts notes. In Japan, life expectancy for women is currently 83 years, while in western Europe the average is 81 for 1995–2000. Current population projections assume that the rest of the world will eventually converge to Japan’s level. “We demonstrated that Japan’s number has the largest distortion. If you eliminate the distortions, Japan ends up looking very much like France or Sweden,” Bongaarts says. The distortion in Japan is larger than in the other countries because the tempo effect depends on the rate at which life expectancy is rising—the more rapid the rise, the greater the distortion. During the last 25 years, life expectancy in Japan has been rapidly rising, outpacing relatively modest gains experienced by the United States and western European countries. Are there limits to life spans? Source Outside funding See Also
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