[Ifeffit] R-factor and reduced chi square

[Kelly, Shelly D.]

Hi Owen,

A test for a significant change in the reduced chi square (RCS).

[(RCS1)^2/(RCS2)^2] - 1 greater than 2 * sqrt ( 2 / degrees of freedom)

If you can not read that, I have this published in J. Phys Chem B, V105
no27 year (2001).  You can down load that paper from my web page
www.mesg.anl.gov.  I guess it is a reasonable test:).  

For most model fits a change by a factor of 2 is needed to be
statistically significant.

Good luck
Shelly

Shelly Kelly                   Bldg 203 RM E113
Skelly at anl.gov              Argonne National Laboratory
630-252-7376                 9700 S Cass Ave
www.mesg.anl.gov         Argonne, IL 60440
 
 
 
> -----Original Message-----
> From: ifeffit-bounces at millenia.cars.aps.anl.gov [mailto:ifeffit-
> bounces at millenia.cars.aps.anl.gov] On Behalf Of OWEN N LI
> Sent: Tuesday, October 04, 2005 1:08 PM
> To: ifeffit at millenia.cars.aps.anl.gov
> Subject: [Ifeffit] R-factor and reduced chi square
> 
> Hi,
>    I understand R-factor and reduced chi square are statistical ways
to
> see if the model is reasonable (R-factor) and if one model is better
> than the others (reduced chi square). But how much should I read into
it?
> 
>     I have model A and B, I believe A is more theoretical sound than
B.
> but when I fit them using IFEFFIT, the R-factor and reduced chi square
> of B is slightly better than A (B: 0.03, 28; A: 0.04, 33). What does
> that tell me? Is my assumption incorrect? Or are they more or less the
> same?
> 
>     Owen
> 
> 
> _______________________________________________
> Ifeffit mailing list
> Ifeffit at millenia.cars.aps.anl.gov
> http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit