[Ifeffit] statistics

Stefano Ciurli stefano.ciurli at unibo.it
Tue Aug 24 10:43:24 CDT 2004


>  > When it comes down to compare fits using different models, which is
>>  the relevant parameter? Chi square (and reduced) or R-factor? I have
>>  fits with smaller chi square and larger Rfactor and viceversa...
>This is definitely a FAQ, so I put the answer at
>   http://cars9.uchicago.edu/cgi-bin/ifeffit/faqwiz?req=show&file=faq08.013.htp


>  > Is it possible that a rationale would be that when the models to
>>  compare have the same number of atoms these parameters go in
>>  parallel? And that when the number of atoms is different one must
>>  rely more on chi square rather than R-factor (or viceversa)?
>I'm not sure I understnad this:  I'd say the number of atoms or
>paths, or anything else that describes the complexity of the
>model, is NOT important. What's important is how well the
>specified variables cause the model to match the data.

I think here below is the answer I was looking for (taken from the link above):

Either of these parameters can be used to compare different fits if 
the number of varibles and data k- and R-ranges are the same for the 
two models.


Stefano Ciurli
Professor of Chemistry
Department of Agro-Environmental Science and Technology
University of Bologna
Viale Giuseppe Fanin, 40
I-40127 Bologna
Phone:	+39-051-209-6204
Fax:	+39-051-209-6203

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