Normalized lifespan inequality: disentangling the longevity-lifespan variability nexus

Area of Science:

• Demography
• Public Health
• Biostatistics

Background:

• Historically, higher life expectancy (average longevity) correlated with lower length-of-life inequality (variability in ages at death).
• This association may be influenced by life expectancy increasing faster than maximal lifespan, compressing age distributions.
• Previous analyses overlooked the bounded nature of human lifespan.

Purpose of the Study:

• To propose a novel approach for measuring lifespan inequality that incorporates the bounded nature of life.
• To re-evaluate the relationship between life expectancy and lifespan inequality using this new methodology.

Main Methods:

• Developed a new metric for lifespan inequality accounting for the upper limit of human life.
• Applied this metric to data from the Human Mortality Database for various countries.

Main Results:

• Observed that lifespan inequality, after initially declining with rising life expectancy, begins to plateau and even increase at higher longevity levels.
• This reversal challenges the traditional inverse relationship between longevity and its variability.

Conclusions:

• The findings suggest that achieving higher levels of average longevity may necessitate accepting greater variability in lifespan.
• This presents complex ethical considerations regarding the distribution of longevity gains in populations.