Rectangularization revisited: variability of age at death within human populations

Area of Science:

• Demography
• Mortality studies
• Public health

Background:

• Human survival curves have historically shown a trend towards rectangularization.
• Rectangularization implies a decrease in the variability of ages at death.
• This trend suggests a compression of mortality, with more individuals living to older ages.

Purpose of the Study:

• To analyze trends in the variability of ages at death in Sweden, Japan, and the United States.
• To investigate whether the rectangularization of survival curves has continued in recent decades.
• To explore potential psychological and behavioral impacts of historical mortality compression.

Main Methods:

• Analysis of life table data, specifically the interquartile range (IQR) of ages at death.
• Longitudinal comparison of mortality variability in Sweden from 1751 to the present.
• Comparative analysis of mortality variability trends in Japan and the United States post-1950s.

Main Results:

• Swedish mortality variability (IQR) decreased significantly from approximately 65 years in 1751 to 15 years by the mid-20th century.
• Since the 1950s, mortality variability has remained relatively constant in Sweden, Japan, and the United States.
• The United States exhibits higher mortality variability compared to Sweden and Japan.

Conclusions:

• The rectangularization of human survival curves, characterized by decreasing mortality variability, has slowed or ceased since the mid-20th century.
• The observed plateau in mortality variability challenges predictions of continued survival curve compression.
• Historical mortality compression may have induced significant psychological and behavioral shifts in populations.