A few comments on this S02 and Ei thing: 1. I am not particularly encouraged by the fact that Matt was just barely able to co-refine S02 and Ei in a copper foil. In many ways a copper foil is a very contrived exafs problem. I would like to see a careful study by someone who understands the statistics well on a wide variety of well-ordered and disordered materials before I would suggest to anyone that they consider reporting both S02 and Ei in the literature. I am sure that S02 and Ei will always be highly correlated and I doubt that, for most problems, they will have reasonable best-fit values despite their large correlations. Of course, I would be pleased to be proven wrong. 2. I don't quite agree with John's assessment of the error bars. The two parameters are almost completely correlated. I don't think it is reasonable to say that two parameters which are that highly correlated and which have values of the same order of magnitude should have error bars of different orders of magnitude. I understand that we have other reasons to know what an appropriate value for S02 should be and so I understand why John wants to state the S02 can be 0.9+/-0.05, but from the vantage point of interpreting the statistics of the fit, you are NOT at liberty to assert an error bar. This is particularly true for a real research problem with difficult sample prep or detector issues. The amplitude really may be something like 0.75 after the fit accommodates such systematic uncertainties. What's more, correlations with the various sigma^2 parameters used in a fit to a disordered material may drive up the error bar on S02 to something like 0.1 or 0.2 or higher. In short, I have to caution everyone reading this list about the dangers of drawing conclusions about hard analysis problems from the results of an easy one like a copper foil. B -- Bruce Ravel ----------------------------------- ravel@phys.washington.edu Code 6134, Building 3, Room 222 Naval Research Laboratory phone: (1) 202 767 5947 Washington DC 20375, USA fax: (1) 202 767 1697 NRL Synchrotron Radiation Consortium (NRL-SRC) Beamlines X11a, X11b, X23b, X24c, U4b National Synchrotron Light Source Brookhaven National Laboratory, Upton, NY 11973 My homepage: http://feff.phys.washington.edu/~ravel EXAFS software: http://feff.phys.washington.edu/~ravel/software/exafs/