Hi Joselaine, On Tue, Aug 14, 2018 at 10:21 AM Joselaine Cáceres gonzalez < joselainecaceres@gmail.com> wrote:
Dear all,
I am new in this group so I don't know if this is the right place to ask about it, but I´d like to know about LCF performed with Athena in XANES data. I had some difficulties in founding information about errors reported by the program. I am working with different techniques and in some cases I have to calculate uncertainty in results reported. In LCF results reported by Athena I don't know how to interpret the errors reported between parenthesis along with each model spectra. In my reports I carefully define if I am reporting the standard deviation of the mean, a combined standard uncertainty,etc. depending each case, the coverage probability, etc. So I need to understand the information Athena is reporting as errors in LCF.
The reported uncertainties are the 1-sigma standard errors. However, the uncertainties in the data are necessary to get the scale of the standard errors correctly, and these uncertainties in the data are (almost always) not supplied for the analysis, so the program has to guess what those uncertainties should be. To do this it follows a common if not-quite-rigorous approach of first asserting that the fit is "good" (otherwise you probably wouldn't care about the detailed scale of the uncertainties) so that reduced chi-square should be 1. That is, it effectively rescales the uncertainty in the data, epsilon, so that reduced chi-square is 1, and uses that to scale the reported uncertainties. Another way to look at this is that the reported uncertainties increase the reported chi-square by reported reduced chi-square, without regard to the value of epsilon used. Hope that helps. Please try to use a separate topic thread in the future, as this question has little or nothing to do with the subject line... --Matt