Life expectancy doesn’t mean that
Tony Cooper has nominated a Bloomberg statistic (being reprinted in NZ) on life expectancy for Stat of the Week.
The `Sunset Index‘ purports to be the average number of years of life after you stop working, with figures ranging from 23.44 for Singapore to 1.49 for Nigeria. New Zealand is somewhere in the middle, with an index of 15.98. It really isn’t credible that Nigerians who leave the workforce at age 50 die an average of 18 months later, so what have they done wrong?
Bloomberg have calculated life expectancy at birth, and subtracted the retirement age, but if you reach retirement, you’ve already avoided dying for a long time. The life expectancy at retirement could be quite different from life expectancy at birth. Since this difference is likely to vary between countries, the `Sunset Index’ won’t even be correct in relative terms.
So, how bad does it get? If you look at life expectancy data for Nigeria you see that, indeed, life expectancy at birth is about 50 years, but that life expectancy at age 50 is 70.7 years for men and 72.6 for women. The true `Sunset Index’ value would be about 21, and Bloomberg are off by a couple of decades.
The error is less severe in other countries: infant and child mortality has a big impact on life expectancy at birth, and in Nigeria about one child in seven dies before age 5. Here are a few corrected values for the Sunset Index
- Singapore: 25
- Nigeria: 21
- Iran: 21
- New Zealand: 20
- USA: 16.5
- Bangladesh: 13
The US is near the bottom of the corrected index because it combines a late retirement age (by Bloomberg’s definition — full Social Security eligibility) with only moderately good life expectancy.
Thomas Lumley (@tslumley) is Professor of Biostatistics at the University of Auckland. His research interests include semiparametric models, survey sampling, statistical computing, foundations of statistics, and whatever methodological problems his medical collaborators come up with. He also blogs at Biased and Inefficient See all posts by Thomas Lumley »
There are some pretty weird claims about life expectancy out there. Anyone who wants to have a go at Stat of the Week can start by typing “expectancy” into the Herald’s search engine. For April we get:
http://www.nzherald.co.nz/lifestyle/news/article.cfm?c_id=6&objectid=10876893 says that today’s adults are 15 years older than their parents. Obviously not literally true and the Herald uses quotes around the word ‘older’.
But what does it really mean? A statistician would think it means that at the same age as their parents today’s adults have 15 years less life expectancy. The article intimates this but it can’t be true since life expectancy has been increasing for generations.
Turns out that it just means that there are as many fat people around now at the age of 40 as there were at the age of 55 in the previous generation. Nothing to do with individual life expectancy at all.
This article http://www.nzherald.co.nz/world/news/article.cfm?c_id=2&objectid=10876725 says for the UK “70.33 years life expectancy men 76.41 years life expectancy women”. Not true.
Should say “70.33 years life expectancy male newborns76.41 years life expectancy female newborns”.
To the Herald’s credit I can’t find fault with these April “expectancy” articles:
http://www.nzherald.co.nz/business/news/article.cfm?c_id=3&objectid=10876733
http://www.nzherald.co.nz/nz/news/article.cfm?c_id=1&objectid=10879156 says “Life expectancy after 65 is about 20 years, and that’s about $350,000 in NZ Super”
11 years ago