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 http://cars9.uchicago.edu/iffwiki/FAQ/FeffitModeling#head-ed63cbd00d0b85def3... can Is the criterion provided by Kelly et al. (2001) J. Phys. Chem. B 105(27) http://www.mesg.anl.gov/pdf/JPC2001samms.pdf 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: http://www.itl.nist.gov/div898/handbook/prc/section3/prc32.htm 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. Aaron