Hello, same old question that emerges again: What formula is used by IFEFFIT to calculate the number of independent points? Does it use the formula 2DkDR/pi? or 2DkDR/pi +1? or 2DkDR/pi +2? And how does it approximate the resulting number to integer? Next: as far as I understand, the conversion from chi^2 to reduced-chi^2 involves dividing the first by the number of degrees of freedom. The latter is obtained by subtracting the number or floating parameters from the number of independent point right?. What if one fixes the value of one parameter, let's say S0^2 to unity? Does the number of parameters includes S0^2 in that case? We consider that it does not. Here is an example. We find with IFEFFIT (we use Dk= 10 (from 2 to 12), DR=5 (from 1 to 6). chi^2 = 87.1 reduced chi^2 = 3.7 parameters: E0, three distances and three sigma^2 we set S0^2 fixed to 1 R-factor: 1.15% The ratio between chi^2 and reduced chi^2 is 23.54, which is not an integer number as we would expect. Plus, this number does not correspond to Ninp -Nvar (31.83 - 5 = 26.83) What are we missing? Sorry if the question sounds silly to most of you. Stefano -- ____________________________________________ Stefano Ciurli Professor of Chemistry Laboratory of Bioinorganic Chemistry Department of Agro-Environmental Science and Technology University of Bologna Viale Giuseppe Fanin, 40 I-40127 Bologna Italy Phone: +39-051-209-6204 Fax: +39-051-209-6203 "Fatti non foste a viver come bruti, ma per seguir virtute e canoscenza" Dante Alighieri - Inferno - Canto XXVI "Ihr seid bestimmt, nicht Tieren gleich zu leben, Nein, Tugend zu erringen und Erkenntnis" "Ye were not form'd to live the life of brutes, But virtue to pursue and knowledge high"