Re: the perils of statistics (math; one-line quippers please skip)

William C. Keel wrote:
How about this: there is a bias in the measured distances of stars
whose parallax values are not many times larger then the measurement
error. Many more stars have underestimated than overestimated
distances (this may be the Lutz-Kelker bias), simply because
there are so many more distant stars than nearby ones.

You know, I must confess a slightly embarrassing thing: I remembered
this example, but I didn't post about it because I couldn't recall the
name of it. I also couldn't be sure I had the right explanation for
the bias, but that's no excuse--I could have written about it and said
I was unsure about the mechanism of the bias.

Anyway, yes, that's exactly the sort of thing that I'm talking about.
Now that people have written about it, it's obvious in hindsight, but
it's not always obvious beforehand.

I wrote about the first example because it involves Little's Law, which
is a pre-eminent principle of queueing theory (one of my specialties).
But in a way, it's too *obvious* a problem--the stellar lifetimes are
so strongly dependent on mass (and spectral class) that it's perfectly
clear which interpretation is meant. But if the dependency were weak,
but still present, it wouldn't have been as clear.

--
Brian Tung <brian@xxxxxxx>
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