Jesus,

On Mon, May 23, 2016 at 7:08 AM, Jesús Eduardo Vega Castillo <jevecas@gmail.com> wrote:

Dear list,

I am back with a new consultation on EXAFS fitting within Artemis.

I have made a fit and obtained a reduced Chi2 value of 391 and R-factor of 0.014 using 9 variables. Then I have added two more paths increasing the number of variables up to 12 and then I obtained a reduced Chi2 of 3039 and R-factor of 0.007.

I am a little surprised by the huge increase of reduced Chi2 while R-factor decreases down to half. 

What could be the cause of this large increase? 

Does it mean that it is not worth to add these new paths?

Reduced chi-square is scaled by dividing by the number of free parameters, (Nidp - Nvarys).  Increasing the Nvarys from 9 to 12 without also increasing Nidp (by adding data k or R range), could definitely make reduced chi-square increase even if the R-factor and chi-square decrease.
 

One of the main uses of reduced chi-square is to determine if additional variables are improving the fit well enough to justify their inclusion in the model.

--Matt

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