Rise, stagnation, and rise of Danish women’s life expectancy

Significance Life expectancy is the most commonly used measure of health status in a population. Life expectancy has increased rapidly in most western populations over the past two centuries. There has been an ongoing debate about the relative contribution of cohort and period effects on a nation’s life expectancy, but few concrete examples of strong cohort effects exist. In this study, we use demographic approaches to study cohort effects on the life expectancy of Danish women. We identify a clear-cut and strong cohort effect: the case of the interwar generations of Danish women. Health conditions change from year to year, with a general tendency in many countries for improvement. These conditions also change from one birth cohort to another: some generations suffer more adverse events in childhood, smoke more heavily, eat poorer diets, etc., than generations born earlier or later. Because it is difficult to disentangle period effects from cohort effects, demographers, epidemiologists, actuaries, and other population scientists often disagree about cohort effects’ relative importance. In particular, some advocate forecasts of life expectancy based on period trends; others favor forecasts that hinge on cohort differences. We use a combination of age decomposition and exchange of survival probabilities between countries to study the remarkable recent history of female life expectancy in Denmark, a saga of rising, stagnating, and now again rising lifespans. The gap between female life expectancy in Denmark vs. Sweden grew to 3.5 y in the period 1975–2000. When we assumed that Danish women born 1915–1945 had the same survival probabilities as Swedish women, the gap remained small and roughly constant. Hence, the lower Danish life expectancy is caused by these cohorts and is not attributable to period effects.