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Re: [Phys-l] calibration



Check out the statistics applet at:
<http://espse.ed.psu.edu/edpsych/faculty/rhale/Statistics/statlets/free/calib.htm>
Using it (and treating the resistivity as the dependent variable in the calibration plot), using the data you provided, I get, for r=62 nano-ohm meters, with the confidence level for the prediction interval set to 68.3%:
p = (33.1 +/- 7.4) %


________________________________

From: phys-l-bounces@carnot.physics.buffalo.edu on behalf of Ludwik Kowalski
Sent: Sun 8/5/2007 5:54 PM
To: Forum for Physics Educators
Subject: Re: [Phys-l] calibration




Aug 5, 2007, at 2:23 PM, Folkerts, Timothy J wrote:


Finding the prediction interval for a linear regression is a little
more complicated than just finding the St Dev of the various points.
It may be convenient to define the uncertainty of p as the standard
deviation of such fluctuations, but it is not the standard practice.
You should perhaps check a stats book for more info on the topic.

A quick run of the data through Minitab suggests that the +/-1 stdev
prediction interval (68.3% confidence level) for r = 0.62 is p =
30.25 +/- 6.5. This is half again as large as the interval you list.
The size of the prediction interval also changes across the range of
the graph.

A couple minor points.
1) The resistivity of Cu is about 10^-8, not 10^+8.
2) I get 4.004, not 4.04 for stdev, but that could be round off error
in the calculations or the original data.

Thanks Tim,
I will replace giga-ohms with nano-ohms today and will check in a
statistics book later. A pedagogically good Internet reference would
be appreciated (for calculating uncertainties from residuals).
_______________________________________________________
Ludwik Kowalski, a retired physicist
5 Horizon Road, apt. 2702, Fort Lee, NJ, 07024, USA
Also an amateur journalist at http://csam.montclair.edu/~kowalski/cf/

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