Hi all I fitted ZnMgO to know whether Mg is sited on Zn position. the method of fitting as following; 1st : to fit with some Mg located on Zn site. 2nd: to fit with some Mg which position is different from Zn cite The parameters for Mg like bonding length, disorder and others were set. When I was fitting, there are only 8 parameters in both two method. So that independent data point and variables are same. Both 1st and 2nd had same R-factor but reduced chi-square of 1st was lager than that of 2nd. It has been known that R-factor is independent of error( uncertainty in the measurement) but reduced chi-squrare is inverse proportional to error^2. So I think that same R-factor and different reduced chi-square for two method mean the fittings of two method are not different, but error used in reduced chi-square is different. I want to know how the error used in reduced chi-square is decided in FEFFIT code.