Life expectancy

Factual Questions
1

How do they come up with figures for life expectancy?

As an example, I have read that the life expectancy for a man in the USA 100 years ago was 47 years. The second US president, John Adams, died in 1826 at the age of 90. Lots of people today don’t even live that long. I couldn’t find life expectancy figures for that time period, but I believe it would be safe to say it would be around the mid 40’s, since it was 47 in 1904. If this is true, it means that John Adams exceeded the life expectancy by around 100%.

Well, today the life expectancy for a man in the USA is around 72 years. But, nobody has ever exceeded that life expectancy by 100%. Nobody has ever lived to be 140, so what’s wrong with this picture?

2

A very significant factor in life expectancies is infant mortality. This changed far more dramatically than the progress in “adult” medicine. A newborn baby could expect a 47 (or whatever) year life on average. Once you survived childhood your chances of achieving an age that is considered decent today increased noticeably. Of course it was still not the same statistically, but really old people were not as rare as the 47 makes one believe.

3

What’s wrong is your understanding of the term “expectancy.”

It’s a fancy term that 's more or less synonomous with “average”, subject to some special initial conditions.

Here’s an example that may make things more clear.

Imagine we’re tracking the life expectancy of some remote village. One year, 10 babies are born. 9 die within the first year and the 10th lives to be 110 years old.

Naturally, it’ll be 110 years before we know this, but this is a long-running experiment with a multi-year research grant :-).

What was the life expectancy of those babies? The formula is total lifespans / headcount =or (110 + (9 * 1)) / 10 = 119/10 = 11.9. Thos ebabies had a life expectancy of not quite twelve years.

Now lets assume the village down the road has better sanitation and of their 10 babies, only 1 dies at age 1, 8 make it to age 75, and the last one still lasts to 110.

Their life expectancy is (1 + (8* 75) + 110) / 10 = 711 / 10 = 71.1.

The real world we live in has the same effect. Most of the gain in life expectancy in the developed world since the 1700s is in the virtual elimination of infant and child-age death. We’ve added a few years on the end through better post-event care for heart attacks and cancer, but the lion’s share of the gain is from fixing infant mortality.
If you’re interested, look up “actuarial table” in google and do some reading. The actual tables are also available from the IRS website, since they’re used for pension calculations.

There are different life expectancies for men, women, different etnic groups, differetn countries, and most interestingly, for different ages.

Going back to our first example village, what was the life expectancy of the 1 surviving child when he/she was 3? Answer:110 years. Apparently paradoxically, as you get older, your personal life expectancy gets longer, not shorter. Why? Becauase the folks born when you did who have already died are removed from the averages going forward.

This math is exactly the core of the life insurance business. They charge you enough premium versus your age to ensure they make a profit on the average customer over his/her average remaining lifetime.

4

Here’s an earlier thread that sorta ties in with yours:

5

I’d like to add that, in addition to decreased infant and child mortality, the widespread use of antibiotics and current sanitary measures have decreased the mortality due to infections considerably.

6

Something I would like to add, besides the explanations about averages and infant mortality.
Historical figures (like John Adams) generally aren’t representative of the lifespan of their contemporaries for two reasons :
-They belonged, in their overwhelming majority, to the uper classes, hence these people were better fed, had a better lifestyle (less streneous work, for instance), etc…which resulted in them having generally a longer life than your average starved and exhausted peasant.
-They generally became famous because they lived long. Someone dying in his 40’s would be unlikely to be elected president, if he was a writer, he would have written much less books and he would have been forgotten, etc… Someone who had a long life would achieve much more things. When you consider the european monarchs of the past, for instance, it’s quite blatant that the most famous ones are generally the ones who lived (and reigned) the longest. It’s generally not because they were exceptionnal kings that they became famous, but because they did a lot of things, amongst them some important things, since they had a long reign.

7

FYI - Let’s not confuse the terms life span with life expectancy. They are not synonymous.

Life Span -

The age of death of the longest-lived member of the species. Madame Calment has defined the life span of the human species as 122 years.
www.bumc.bu.edu/Departments/PageMain.asp

The longest number of years any member of a species has been known to survive.
www.crab.rutgers.edu/~deppen/448glossary.htm

The maximum age that human beings could reach under optimum conditions.
www.planetwire.org/glossarylist.php

Life Expectancy -

The average number of years remaining for a person of a given age to live as shown on the mortality or annuity table used as a reference.
www.new-york-life-insurance-quotes-company.com/glossary.html

The average number of years remaining for a person of a given age to live as shown on the mortality or annuity table used as a reference. (LI)
www.insweb.com/learningcenter/glossary/life-l.htm

The number of years that an average person of a given age may be expected to live, according to mortality tables (CMD 1997).
www.who.int/environmental_information/Air/Guidelines/ann3.htm

The average number of years that an average person of a given age may be expected to live, usually as determined by mortality tables.
www.bumc.bu.edu/Departments/PageMain.asp

The average number of years remaining for a person of a given age to live as shown on the mortality or annuity table used as a reference.
www.termlifepros.net/glossary.html

Average number of years a newly born child can expect to live.
www.soton.ac.uk/~engenvir/glossary.html

The average number of years a person can expect to live.
www.kzpg.com/Lib/Pages/Tools/glossary.html

The average number of years of life remaining for a group of persons given age according to a particular mortality table
www.ltcinsurance.com/Glossary_of_long_term_care_Terms.html