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Re: Systematic vs. Random



Hi all-
Tim doesn't give enough information to answer the question. If
the uncertainty in the intercept is large enough to include the zero
point, then one can't use the y-intercept to distinguish random from
systematic uncertainty - a combination could account for the difference.
If the uncertainty in the intercept excludes the zero point with
high probability, then one needs to examine possible sources of systematic
error.
If you can exclude systematic error with high probability, then
you need re-examine the theory that you are using to interpret the data.
Regards,
Jack

Adam was by constitution and proclivity a scientist; I was the same, and
we loved to call ourselves by that great name...Our first memorable
scientific discovery was the law that water and like fluids run downhill,
not up.
Mark Twain, <Extract from Eve's Autobiography>

On Tue, 29 Aug 2000, Tim Burgess wrote:

During a post lab discussion yesterday students were presenting
the results of the standard pendulum lab (l vs. T).

A student asserted that because the test plot of T^2 vs. l by another
team resulted in a y-intercept that was about 4% of the maximum T^2
value then there was probably a "systematic error". My first reaction
(while the students discussed this) was that this was not true. The bell
rang. All left. I will see them again last period today.

I would like to get the general thoughts some on this list might have
regarding the validity of making the "systematic error" assertion based on
y-intercept value (combined with 9 well fitted data points).

Thanks

Tim