“Human life is unlimited – but short”

June 7, 2018

(This article was originally published at Statistical Modeling, Causal Inference, and Social Science, and syndicated at StatsBlogs.)

Holger Rootzén and Dmitrii Zholud write:

This paper studies what can be inferred from data about human mortality at extreme age. We find that in western countries and Japan and after age 110 the risk of dying is constant and is about 47% per year. Hence data does not support that there is a finite upper limit to the human lifespan. Still, given the present stage of biotechnology, it is unlikely that during the next 25 years anyone will live longer than 128 years in these countries. Data, remarkably, shows no difference in mortality after age 110 between sexes, between ages, or between different lifestyles or genetic backgrounds.

This relates to our recent discussion, “No no no no no on ‘The oldest human lived to 122. Why no person will likely break her record.'”

I’ve not looked at Rootzén and Zholud’s article in detail, nor have I tried to evaluate their claims, but their general approach seems reasonable to me. The rule of thumb of a 50% mortality per year at the highest ages is interesting.

That said, I doubt that we can take this constant hazard rate too seriously. My guess is that an empirically constant hazard rate is an overlay of two opposing phenomena: On one hand, any individual person gets weaker and weaker so I’d expect his or her conditional probability of death to increase with age. On the other hand, any group of people is a mixture of the strong and the weak, which induces an inferential (“spurious,” as Feller called it) correlation. Maybe these two patterns happen to roughly cancel out and give a constant hazard rate in these data.

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