[Ifeffit] errors in bond lengths

[George Sterbinsky]

Hello,

As is well known, EXAFS is more accurate at determining relative changes in
bond lengths than absolute changes in bond lengths due to cancelation of
systematic errors in relative comparisons. When comparing the relative
changes in bond lengths determined from EXAFS fits, as one might for a
temperature series for example, is it appropriate to use the uncertainties
returned by Artemis?

My question arises in part from Phys Rev Lett vol. 100 pg. 055901 (2008),
where the authors state that errors for changes in bond length in a
temperature series were determined by empirical means rather than
statistical means. This then raises the question as to if the authors
believe that statistical means would overestimate the error. My inclination
is to think that the uncertainties reported by Artemis would be appropriate
because of the scaling by the square root of reduced chi squared. However,
I want to see what others think about this before committing to it.

Thank you,
George
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