The Emergence and Proliferation of Centenarians

Abstract

Between the 1950s and the 1980s the number of new centenarians in western Europe and Japan grew at an annual rate of about 7% doubling every decade. However the multiplication of centenarians must be attributable to some combination of earlier changes in natality migration and mortality. In particular the rate of growth in the number of 100-year-olds can be decomposed into the sum of the rate of increase in births 100 years ago the rate of decrease in the effects of net emigration and the rate of improvement in survival from birth to 50 50 to 80 and 80 to 100. In the Scandinavian countries the cohorts born in the 1880s were larger than those born in the 1870s. The predominant cause was greater survival from age 80 to 100. Over most of the course of human existence life expectancy hovered between 20 and 30 years; even in western Europe life expectancy did not reach 40 until after 1800 and 50 until after 1900. In many countries female life expectancy now exceeds 80 years; in Japan female life expectancy is above 82. Under the most brutish conditions with a life expectancy at birth of 19 years the odds against attaining age 100 may have been 20 million to 1. Under current conditions in Japan and Sweden 2 women in 100 will survive a century or more. This 400000-fold rise in survival chances is largely attributable to an increase in the probability of an octogenarian becoming centenarian. The emergence and proliferation of centenarians dramatically illustrates the improvement in the life chances of octogenarians and nonagenarians. If the present pace of improvement in old-age survival persists it will be as likely for a child today to reach age 100 as it was for a child born 8 decades ago to reach age 80.