# What's my statistical lifespan?

I’ve been pondering this for a while: of the people who live to a certain age, what is their average lifespan?

Lifespan is a fickle statistic for me. Usually it’s cited as “average lifespan,” but gives no indication of what data points are thrown out. For instance, if you’ve got 5 people and 4 of them live to 80 and one dies at birth, the average lifespan is 64. As I’ve seen statisticians do, they use the median age which is 80. If someone in that micro-society didn’t die at birth, they’d expect the average lifespan to be more like 80 than 64 because they would throw away the data points of the people who died younger than them.

I’ve seen statistics which state the average lifespans for Americans as around 75 or so (both men and women). Since I’m part of the population who didn’t die at birth or in an accident, what’s the average lifespan of all people who lived to at least 28? When I hit the average lifespan of people born in 1970, shouldn’t half the people born that year be alive, and if that number is higher than half, does that mean my time is up?

Does anyone know of a source for this information?

You are correct to read any statistics carefully, and to be alert to the difference between the average (mean), the median, and the mode (most frequent occurrence.)

Most life expectancy statistics are based on data from insurance companies, who pool their information thru studies conducted by the Society of Actuaries, so that the data base includes many hundreds of thousands of lives.

The number cited most often in newspapers is “life expectancy from birth”, although “birth” is usually defined as being a few months old. Infant mortality tends to be highest in the first few days after birth, and so those deaths are usually excluded from the general statistics – your example is right on target.

Because of the large number of lives in the sample, and because of eliminating birth-related infant mortality, the difference between the mean and the median is pretty much insignificant.

The only table I have available at the moment is the 1983 Group Annuity Mortality, which gives the following life expectancies. What I’m copying below shows, if you have attained age 20, then the expected (average) remaining years are 55.2 for males, 61.6 for females, for a total life expectancy of 75.2 for males, 81.6 for females.

20 - 55.2 (M), 61.6 (F)
30 - 45.6 (M), 51.8 (F)
40 - 36.0 (M), 42.1 (F)
50 - 26.9 (M), 32.6 (F)
60 - 18.8 (M), 23.5 (F)
70 - 11.9 (M), 15.3 (F)
80 - 7.0 (M), 8.9 (F)
90 - 4.1 (M), 4.7 (F)

By the way, the other statistic to look for is the survival rate. If you are a male age 30, the odds of your surviving until age 80 is 40.3%; if you are a female age 30, the odds of your surviving until age 80 are 62.9%.

The major decline in mortality occurs at age 40 for both males and females, so if you’re thinking of buying life insurance with a fixed lifetime premium, start it before age 40.

I will try to get more recent statistics in the next day or two.

Other mathematical-type comments: the data is usually smoothed in five-year brackets; that is, the raw data may show a higher expectancy at age 70 than at age 69, which is silly; such minor glitches are assumed to be due to sampling errors, and smoothing techniques are used. Assumptions are made about deaths being spread evenly through the year, although that’s not actually true – more deaths occur (especially at older ages) in the month immediately after a big birthday (such as 80 or 90)… usually interpreted as people “hanging on” to reach a milestone date and then sort of “giving up.”

Sorry, you asked for a source – I’d suggest the Society of Actuaries, 47 Martingale Road, Suite 800, Schaumburg, IL 60173. Phone is 847-706-3500, and web page is http://www.soa.org

Same resource for Canada; if you’re in the U.K., the Institute of Actuaries (I don’t have their address handy) and if you’re in a different country, the equivalent body.

Forget that mathmatical, statistical stuff. If you want to know your life expectancy, try the death clock. It is much more accurate.

## http://www.deathclock.com

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Hmmm…14, that seems like a small number, now 5…4…3…2…1…AAACCCKK!!!