On Thu, 27 Apr 2000 14:43:08 +0200, Selim Issever
<[EMAIL PROTECTED]> wrote:
> Dear all,
>
> I measure a physical quantity about 100 times. I am not interessted in the
> mean value but the spread (the RMS) of this quantity. I can calculate the RMS
> easily, but I also need the error on the RMS. Could you give me a hint how to
> calculate the error on the rms?
>From your description, there is no reason to think that there has to
be any "error" at all.
You have a set of measures. The are somewhat spread, for real,
physical reasons. The dispersion looks like gaussian, but it would
not have to be that shape. (How were the points selected? Why were
they selected?) If you want to describe the spread of that set of
measures by the RMS, you may do so -- though it might be more useful,
it seems to me, to describe the extremes and the conditions that
produced them.
Why do you think there may be error in the measurements, and how would
you detect it if there were?
>
> May be I should add, that the spread is not due to the measurement, but real.
> A good example would be a metal bar, which expands and shrinks due to
> stochastic temperature effects. The value I would be interessted in, is the
> _length_variation_ and an _error_estimation_ for this value.
>
> The distribution of the quantity I am looking at could be approximated by an
> gaussian (just in case it eases the discussion). At least it looks like a
> gaussian, when I histogram it.
--
Rich Ulrich, [EMAIL PROTECTED]
http://www.pitt.edu/~wpilib/index.html
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