The Mortality Fallacy


No, this isn’t a spooky Halloween post. So why the tombstone? It’s because I want to rant about one of the most common errors people who should know better make when it comes to life expectancy.

How many times have you heard that a hundred years ago most people died–pick a number–before they were 45, 50, 60?  Yet maybe you had grandparents who lived into their 70s, and if you visit an old cemetery and look at the dates on tombstones, you’ll find lots of people who lived very long lives.

OK, I’m not disputing that Americans in the 21st century can expect to live longer than their counterparts in the 20th century. But there’s a popular fallacy about life expectancy. It has to do with looking at “average” life expectancy, something that was seriously skewed by high infant mortality rates in the past.

The best way to look at life expectancy is to take the view of actuarial tables, which look at it this way: in a given year, someone who’s 20 years old can expect to live another X years while someone who’s 40 years old can expect to live another Y years, etc.

So here’s what it looked like in 1900:

A baby born in 1900 could expect to live another 48 years. Does that mean most people died before age 50? No. This number reflects the high probability of the child dying in infancy or early childhood.

A child aged 10 in 1900 could expect to live another 50 years.

Someone aged 30 in 1900 could expect to live another 35 years.

(Statistics are from the National Bureau of Economic Research.)

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Quotable

Those who do not want to imitate anything produce nothing.

–Salvador Dali

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