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Old December 13th 16, 09:44 AM posted to sci.astro
Martin Brown
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Posts: 1,707
Default 1) the negative paraxes...

On 12/12/2016 06:42, Poutnik wrote:
Dne 11/12/2016 v 22:50 Mike Dworetsky napsal(a):
Poutnik wrote:

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.


Positive and negative noise values are equally unphysical.


But you only know for certain that the negative values are unphysical
the positive ones could be real to within some measurement error. Later
more refined experiments may be able to narrow down the error bars.

BTW The speed of light in vacuum with error bars displayed makes
salutary reading for anyone over confident in good experimental method.
Essentially one famous experimenter applied a partial vacuum correction
in the wrong direction for a new method and everyone copied him until an
even more exquisitely sensitive technique gave a different answer. So
for a couple of decades the speed of light was very precisely wrong due
to unrecognised systematic errors. The graph was in an introductory
relativity book but I forget which one - anyone recognise it from this?

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.


IMHO He should truncated all measurements
with zero belonging to CI of the measurement (mean) value,
as with statistically insignificant difference to zero.


No. Provided that it is stated somewhere what the limits of detection
for the method actually is then the value determined even if it is
negative is more useful to later researchers than a "below LOD" flag.

--
Regards,
Martin Brown
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