Comment by pourush
13 years ago
Could you explain what you mean by "statistical blip"? It seems odd to say that, I mean, wouldn't it imply that there's interference from improper measuring, or interference from variables gone unnoticed, or interference from variables that are irrelevant? I'm probably reading it wrong, but it seems such a bizarre thing to say.
What I mean is, Poisson distributions don't look like normal distributions if lambda is low - there's a long tail.
There's about 500,000 centenarians (thanks bitwize for the spelling) in the world. That's about 0.01%. In a town of 10,000, that's an average (lambda) of 1. About 36% of such towns will have no centenarians, 36% will have one, 18% will have 2, 6% will have 3, 1.5% will have 4, and there's a long tail with 5 (0.3%), 6 (0.05%) or more.
It doesn't seem logical that most towns will have 0 or 1 centenarians, and some will have 5 or more, but it's just the way the numbers work.
If you pick a higher lambda (for example, the number of 50 year olds) it looks like a normal distribution. If some place has 2X the number of 50 year olds, there will be a good reason. If you pick a higher lambda (the number of people who survive incurable cancer) it looks even wackier, and it's very hard to draw conclusions.
What I'm saying is, it's hard to draw conclusions when you are looking at rare events, because there can be so much variation.
Thank you for that explanation. I believed you had said that studying what was different for centenarians - or similar biological anomalies - in a blue zone was quite possibly useless, but it seems that wasn't the case.
It could be a sample size effect. There are all these old people there, but how many? It may have nothing to do with the island, they may all have just been lucky and had a streak of heads in the coin flip game. This is especially likely since the researchers are looking all over the world for these small pockets of longevity.
Why don't you ever hear about these things in larger areas? Certainly different countries have very different lifestyles. What's different is that bigger regions have a smaller chance of a freak streak of long lived individuals as a proportion of the population (though as an absolute value, you'll probably find more).
I suspect "blue zones" will regress to the mean after these individuals in the study die, but you can never be sure. If they don't, maybe the islands do have an effect (or maybe they started to attract immigrant older people seeking longevity).