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The paper "Living too long" by Guy C Brown published in 2015 has the following paragraph:

Human life expectancy has been increasing at a rapid rate. Better health care and hygiene, healthier life styles, sufficient food and improved medical care and reduced child mortality mean that we can now expect to live much longer than our ancestors just a few generations ago. Life expectancy at birth in the EU was about 69 years in 1960 and about 80 years in 2010, which corresponds to a rate of increase in life expectancy of 2.2 years per decade. If this rate of increase remains unchanged, as it has for the last century, then someone born in the EU today would be expected to live about 100 years.

My calculation of the life expectancy of someone born in the EU in 2015, based on the statement that "Life expectancy at birth in the EU was about 69 years in 1960 and about 80 years in 2010, which corresponds to a rate of increase in life expectancy of 2.2 years per decade." was approximately 81.1 years which is not "about 100 years".

Could the explanation be that "someone born in the EU today would be expected to live about 100 years" is not equivalent to "life expectancy at birth in the EU is about 100 years"? Or have I made some other error?

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    are you asking us to check the math? or what do you mean by "invalid conclusion" Jun 3 at 21:08
  • It uses "about" - meaning approximately - three times in the "math" part. Do you see the figures as "approximately" incorrect then? Jun 3 at 21:49
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    Likely reading about different ways life expectancy can be defined will help, see en.wikipedia.org/wiki/Life_expectancy for example. It's perhaps also worth noting that this isn't really a conclusion of the paper, just an interpretation of some figures presented in the introductory section. Jun 3 at 22:32
  • @SecurityEveryDay still need clarification of what exactly you are asking Jun 3 at 22:43
  • @aaaaasaysreinstateMonica I edited the question. Is it clear what I am asking now? Jun 3 at 23:19
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Short answer

The source does not make the claim "2015 life expectancy at birth in the EU will be 100 years". It makes a more vague statement "would be expected to live about 100 years". There could be an error, but more likely this is simply a discrepancy between period and cohort life expectancy, and the author assumes readers will recognize the distinction.

Longer answer

81.1 years would be the life expectancy of someone born in 2015 in 2015. There are different versions of life expectancy, but we can assume they are talking about period life expectancy in the first part, and cohort life expectancy later (quote from the Wikipedia link prior, bold mine):

Cohort LEB is the mean length of life of an actual birth cohort (all individuals born in a given year) and can be computed only for cohorts born many decades ago so that all their members have died. Period LEB is the mean length of life of a hypothetical cohort[1][2] assumed to be exposed, from birth through death, to the mortality rates observed at a given year.[3]

So, the life expectancy of someone born in 2015 by the period measure is from death rate of infants, the death rate of 40 yr olds, 60 yr olds, etc, in 2015, and then integrated over a lifetime.

If life expectancy continues to increase, then people in the 2015 cohort will die on average later than they were predicted to based on the 2015 rates. For someone born in 2015, their cohort won't experience the death rate of a 70 year old in 2015, they'll experience the death rate of a 70 year old when they are 70, that is, in 2085.

This is kind of just a throwaway by the author to say "about 100" and there is no definitive methodology to check the perfection of their math, but it seems approximately correct if life expectancy really did continue to increase at a rate of 2.2 years per decade. Whether it's reasonable to assume that increase is another matter, of course.

You can't know the cohort life expectancy until those folks actually die, but the author is estimating the mean will be about 100.

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