[Ifeffit] statistical vicissitudes

Aaron Slowey aaron.slowey at gmail.com
Thu Jan 18 16:49:38 CST 2007

Hello -

The use of R-factors and reduced-chi-squared values, it's computations
by IFEFFIT have been made clear by past writings, but the use of
reduced-chi-squared as a comparative statistic has not, to my
knowledge, been completely well-documented.

Not withstanding the three disconnects between classical statistics
and the realities of EXAFS mentioned in the IFEFFIT faq section



Is the criterion provided by Kelly et al. (2001) J. Phys. Chem. B 105(27)


namely, redchi-sq_1 / redchi-sq_2) - 1 > 2 * (2 / deg_of_freedom)^0.5,

derived from the F-test formalism and, if so, how?

I tried to derive the above equation based on the F-test formalism
provided by NIST:


but was unsuccessfull. The Kemner et al. paper referenced by Kelly et
al. to explain the statistical basis for the above equation does not
clearly do so.

I request that someone please provide a reference to a *first
principles* basis for criteria to compare reduced-chi-square values of
alternate EXAFS fits.


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