American centenarians

A subthread in the comments to Erik’s Jimmy Carter obituary raised the question of how likely it is that any of us will see another centenarian president. The stats quoted in that subthread were way off, and I don’t want to let 2024 slip away without grappling with this important hypothetical issue.

Less facetiously, the veritable explosion of centenarians — and of more pragmatic significance, really old people generally, say 85+ — has a lot of social implications.

First, the odds that one of the currently living men who have been or are president or both (yeech) will reach 100 are actually not too bad at all. Using actuarial statistics, which of course are not necessarily going to be that accurate given an N = 5, but that’s what we’ve got to work with here, the odds that one 82 year old man, three 78 year old men, and a 63 year old man will yield at least one centenarian eventually are 9.1%. A possibly counter-intuitive fact is that Obama has in general actuarial terms the lowest odds of reaching 100, simply because he’s a lot younger than the other four. The individual odds for these five men of reaching 100 are 2.35% (Biden), 1.9% (the three 78 year olds) and 1.3% (Obama).

This assumes that the age-adjusted mortality rates of old people will not decline over the next 18 to 37 years, which if history is a guide is an assumption that will certainly be wrong, so the 9.1% estimate is likely to be far too low, remembering again that this is all pretty loosey goosey, statistically speaking, but hey it’s the holiday week at the end of the year.

Speaking of which, the non-trivial issue here is that the very sharp decline in age-adjusted mortality rates among the elderly over the past several decades has produced a massive increase in the total number of centenarians in the US. 1n 1970, the Census Bureau estimates there were about 4,800 centenarians in the country. That figure is projected to increase by close to 100-fold in the next 30 years! (It’s currently already more than twenty times larger). About one in every 300 people born in the 1920s have or will reach the age of 100, but that figure will increase to about one in 50 for people born in the last decade, assuming age adjusted mortality rates don’t continue to decline, which again they almost certainly will.

And of course if we have close to a half million centenarians 30 years from now, we are going to have many many millions of people in their late 80s and 90s. In other words, the Boomers aren’t going away for a long long time, which probably means among other things that, Paul McCartney, Jimmy Page, and Mick and Keith will still be significant pop culture figures on their 100th birthdays, which is not something anybody would have predicted in 1968, probably.