[Ifeffit] Chi in arthemis

Scott Calvin SCalvin at slc.edu
Tue Aug 18 15:07:44 CDT 2009

Hi euG,

I don't report chi-square at all. I know that the official IXS reports  
suggest it, but until the question of what to use for the measurement  
uncertainty is adequately addressed within the community, it seems to  
me that the number is not very meaningful in an absolute sense. It is  
meaningful, however, for comparing fits on the same data. (I do report  
R-factors to give some sense of closeness of fit.)

On the other hand, uncertainties in fitted parameters are calculated  
in a highly defensible way and should be reported. If the  
uncertainties are large for parameters that are of interest to you,  
then that is indicative of a problem in the fit and should not be  
swept under the rug.

--Scott Calvin
Sarah Lawrence College

On Aug 18, 2009, at 4:02 PM, Eugenio Otal wrote:

> Hi all,
> I see that the reports of the fits a perform in arthemis have Chi  
> really big. The fit is really good and the Chi should be closer to 1  
> than to 100.
> The problem, is what should I report as the Chi. Uncertain in delr  
> or ss have the same problem, are big like the results.
> I found the topic in the list but not a good answer to what should I  
> report.
> Thanks, euG

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