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Re: systematic error and statistical error



Hi Ludwik,
it seems to me that what you call here 'systematic error'
is actually a bias. Aren't you mixing both concepts?

On the other hand, one can never get rid of systematic
sources of errors: The finite precission of any apparatus
introduces such a systematic error. And this is unavoidable.
Information on this source of systematic error is usually given
by the manufacturer, who has done a calibration of the apparatus.
In the absence of this information, the minimal interval you can
measure with your apparatus seems to me a reasonable estimate
(lower bound, if you want) for this systematic error.

Regards,
Miguel A. Santos
msantos@etse.urv.es


On Tue, 10 Oct 2000, Ludwik Kowalski wrote:

Date: Tue, 10 Oct 2000 13:07:51 -0400
From: Ludwik Kowalski <KowalskiL@MAIL.MONTCLAIR.EDU>
Reply-To: "phys-l@lists.nau.edu: Forum for Physics Educators"
<PHYS-L@lists.nau.edu>
To: PHYS-L@lists.nau.edu
Subject: Re: systematic error and statistical error

My recollection is that only statistical errors are given in
real scientific publications, that is when the true value is
really unknown. If a true value is know then it is used
to eliminated the systematic error. There is no way to
determine a systematic error without comparing our
results with the accepted results. In teaching, on the
other hand, the true value is usually known and it is
OK to ask student to use it. I am not aware of any
rules about ways of reporting it. Do what you prefer.
Ludwik Kowalski

"William J. Larson" wrote:

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I want to tell my students:
"The results of your measurement should be reported in the form:
x = average of all the x-values ± systematic error ± statistical error."

Not that it really matters, but is that the right order or is it:
statistical error ± systematic error? Or is there no "right" order?

This is pretty embarrassing - obviously I don't DO physics
anymore :-(

Dr. William J. Larson
Bill_Larson@csi.com
Institut Monte Rosa
Montreux, Switzerland

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<DIV align=justify>I want to tell my students:</DIV>
<DIV align=justify>"The results of your measurement should be reported in the
form:</DIV>
<DIV align=justify>x = average of all the x-values ± systematic error ±
statistical error."</DIV>
<DIV align=justify>&nbsp;</DIV>
<DIV align=justify>Not that it really matters, but is that the right order or is
it:</DIV>
<DIV align=justify>statistical error ± systematic error? Or is there no "right"
order?</DIV>
<DIV align=justify>&nbsp;</DIV>
<DIV align=justify>This is pretty embarrassing - obviously I don't DO physics
</DIV>
<DIV align=justify>anymore :-(</DIV>
<DIV align=justify>&nbsp;</DIV>
<DIV align=justify>Dr. William J. Larson<BR><A
href="mailto:Bill_Larson@csi.com";>Bill_Larson@csi.com</A><BR>Institut Monte
Rosa<BR>Montreux, Switzerland<BR></DIV>
<DIV align=justify>&nbsp;</DIV></BODY></HTML>

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