Skewness and kurtosis explain much of lifespan disparity

What the study found: Lifespan disparity, which measures variation in ages at death, can be expressed using standard statistical measures such as skewness. The study found that remaining life expectancy still contributes the most to lifespan disparity, but its share has declined over time as variance, skewness, and kurtosis have become larger shares.
Why the authors say this matters: The authors conclude that adding skewness and kurtosis gives new insights into mortality compression and lifespan variability trends. The study suggests these measures help describe how age-at-death patterns are changing.
What the researchers tested: The researchers analyzed 7,408 life tables from the Human Mortality Database, covering 41 countries from 1751 to 2019. They examined how the moments of age-at-death distributions relate to lifespan disparity and its trends.
What worked and what didn't: The study reports that shifts in skewness have changed mortality patterns, with distributions including older ages showing increasingly positive skewness and those including younger ages showing increasingly negative skewness. It also reports that recent trends are moving toward more symmetric distributions, and that kurtosis patterns suggest a persistent fraction of deaths at the extremes, with a plateau in the number of centenarians. For adult populations aged 30 and older, about 95% of life disparity values were determined by the first four standardized moments of the age-at-death distribution.
What to keep in mind: The abstract does not describe limitations beyond the scope of the data used. The findings are based on historical mortality tables from the Human Mortality Database and on adult populations for the 95% result.

Key points

• Remaining life expectancy contributes most to lifespan disparity, but its share has declined over time.
• Variance, skewness, and kurtosis now account for larger shares of lifespan disparity.
• Older-age distributions show increasingly positive skewness, while younger-age distributions show increasingly negative skewness.
• Kurtosis patterns suggest a persistent fraction of deaths at the extremes and a plateau in centenarians.
• For adults aged 30+, about 95% of life disparity values are determined by the first four standardized moments.