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@anl.gov Argonne National Laboratory 630-252-7376 9700 S Cass Ave www.mesg.anl.gov Argonne, IL 60440

-----Original Message----- From: ifeffit-bounces@millenia.cars.aps.anl.gov [mailto:ifeffit- bounces@millenia.cars.aps.anl.gov] On Behalf Of OWEN N LI Sent: Tuesday, October 04, 2005 1:08 PM To: ifeffit@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@millenia.cars.aps.anl.gov http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit