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Old December 11th 16, 09:50 PM posted to sci.astro
Mike Dworetsky
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Posts: 715
Default 1) the negative paraxes...

Poutnik wrote:
Dne 11/12/2016 v 17:57 Mike Dworetsky napsal(a):

Your suspicion is correct. If you have a list of parallaxes of very
distant objects, so that their parallaxes are on average much smaller
than your limit of detection, then the errors of parallax are
distributed normally, with a bell-shaped curve plotting the likely
distribution of values around a mean of nearly zero. Hence we expect
there to be approximately half of those published parallaxes with
values less than zero and half with values more.

The question remains,
why the data with parallax value within the measurement error
is not replaced by an appropriate note,
instead of publication of noise.

For exactly the reason I stated in the part of my reply that you snipped:
Negative values are unphysical, but form the part of the statistical
distribution of values that happen to lie below zero when the mean is close
to zero.

Imagine that someone plotted a graph of, say, a spectrum (with low S/N), and
wherever the plotted flux was below zero, they simply truncated it. Would
you be happy with that? I wouldn't.

Mike Dworetsky

(Remove pants sp*mbl*ck to reply)