EDINBURGH – A century ago, children outnumbered the elderly by as much as ten to one in most European countries. Today, there are as many people over the age of 65 as there are under the age of 16. In the United Kingdom, roughly one in six people is 65 or older, compared to one in eight Americans, and one in four Japanese.
This shift has been powered by declining birth and infant-mortality rates in the first half of the twentieth century, together with rising life expectancy in recent decades. Whatever the causes, many are concerned that, in the coming decades, rapidly aging populations will increasingly strain health, welfare, and social-insurance systems, putting unsustainable pressure on public budgets.
But, while such fears are not entirely unfounded, discussions about population aging tend to exaggerate the trend’s scale, speed, and impact, owing to a fundamental misperception about how populations grow older. Unlike people, populations do not follow the life cycle of birth, aging, and death. And, while a population’s age distribution may change, age becomes an unreliable way to measure a population’s productivity as lifespans increase.
Age has two components: the number of years a person has lived (which is easy to measure for individuals and populations) and the number of years a person has left to live (which is unknown for individuals, but possible to predict for populations). As mortality declines, remaining life expectancy (RLE) increases for people of all ages. This distinction is crucial, because many behaviors and attitudes (including those that are health-related) may be linked more strongly to RLE than to age.