# Older people have longer average life expectancy

Via Lubos Motl, I today came across another wonderful piece of recent scientific research. From the Harvard University Gazette, after a detailed statistical analysis the National Center for Heath Statistics has concluded the following,

the older you are today, the greater the age you are likely to reach.

The reason for this?

Because they [older people] have already dodged the mortal dangers that do in younger people: infant mortality, violence, and auto wrecks.

What an insightful interpretation of a complete load of crap. Allow me to offer my own interpretation. Assume average life-expectancy is not changing with time. Then, for any age distribution of the population, the average life-expectancy of a subset of that population over a particular age, will necessarily be higher than the average life-expectancy of the entire population. Next, if average life-expectancy is increasing over time (which it is, as a result of improved nutrition, medicine etc.) then on average, people born later can expect to live longer than people born earlier. Thus, the only explanation for the observed trend, that the older you are, the longer you are likely to live, is that the statistics are dominated by the first effect, that of post-selection pushing up the average.

What a brilliant piece of research. Publish it in Nature.

## One thought on “Older people have longer average life expectancy”

1. D’oh! I’d actually wondered about that trend, and checked it on the Australian Bureau of Statistics, and it holds in Oz too.

I think what it more interesting is the rate of change of life expectancy with age – if I recall, there was a blip at early ages (I guess infant mortality), and (among others) an increase at the high end – living to 90 gives you a good boost in expected years to come, more (in some percentage-wise sense, I guess) than say living to 80, etc. I don’t really know how to explain the last one – perhaps if you’re tough enough to live to 90, you’re tough enough to go further, whereas at 80 your average is messed up by all those who are still going to die soon.

But it’s been a while since I looked at that, so people should do their own research!