Life Expectancy and You (for non-demographers)

It is worth noting, if you use this life expectancy calculator, that the accuracy of your statistical death(??) (“There’s a big difference between statistically dead and all dead! Statistically dead is slightly alive!”) is contingent upon you living out the rest of your life in the year 2015 on repeat, à la Groundhog Day.

Why? Life expectancy as used here is a period measure – it tells us what someone’s average lifespan would be if they were subject to this year’s (or period’s) age-specific mortality rates every year. This might be a good estimation of actual remaining life if mortality rates weren’t changing, but they are.

They aren’t changing that quickly, so an estimate of remaining life for 75-year-olds based on current mortality might not be so far from what we’ll actually see happen to that cohort. But the younger you are, the farther off it’s likely to be. Life expectancy at birth is the wrongest of all. “A boy born now (age 0) can” ABSOLUTELY NOT “expect to live to 76,” despite what WaPo says; not only will mortality patterns change over his lifetime, but we could also talk about whether averages are a good predictor of individual experience.

For example, in this paper by Vladimir Canudas-Romo, Swedish life expectancy improved significantly over the course of the late 19th century, as increased infant survival pulled the average up, but the modal age at death was pretty flat. (Check out Figure 2.) The less variance there is in the age at death – the more we all tend to make it to old ages rather than dying in infancy – the more closely life expectancy at birth will align with median and modal lifespans, but this is a great illustration of what numbers like life expectancy do and don’t tell us.

tl;dr: Any time someone uses “life expectancy” and “how long you can expect to live” together, they are wrong.


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