[Ifeffit] R-factor

Alison L Costello acostell at unm.edu
Wed Jul 6 15:10:40 CDT 2005

Thanks to all for taking the time to discuss my concerns. 
 To clarify, both fits were done with exactly the same 
parameters. So, I believe Bruce's description (below) best 
explains what is happening.  I also realize that my 
R-factors are rather large compared to the norm for very 
well-ordered systems.  I am, however, fitting protein data 
that are characteristically not well-ordered.

Thanks again for your time, concerns, and suggestions. 
 They were all much appreciated.

Alison Costello
University of New Mexico
MSC03 2060
1 University of New Mexico
Albuquerque, NM 87131

>Viktor and Anatoly are most certainly correct that you parameters should be
>consistent between the k and q fits. That is probably the bottom line in this
>But as long as we are talking about R-factors....
>In the example you give here, it seems to me that you are seeing the interplay
>of two different aspects of the calculation. In the k-space R factor, the
>R-factor includes high frequency Fourier components -- both structural and
>noise. (That is, the R factor considers differences between data and theory
>and the data includes high frequency pieces in the k-space fit.) The q-space
>fit has had the high frequency stuff removed, but has the factor of two given
>that it's a complex function. Those two competing parts of the calculation
>should explain away the values you quote.

>Bruce Ravel ----------------------------------- bravel at anl.gov -or-
>ravel at phys.washington.edu
>Environmental Research Division, Building 203, Room E-165
>Argonne National Laboratory phone: (1) 630 252 5033
>Argonne IL 60439, USA fax: (1) 630 252 9793
>My homepage: http://feff.phys.washington.edu/~ravel 
>EXAFS software: http://feff.phys.washington.edu/~ravel/software/exafs/

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