Hi Pushkar,

On Mon, Nov 23, 2015 at 11:28 PM, pushkar shejwalkar <
pshejwalkar2...@gmail.com> wrote:

> Dear Matt,
>   Thank you very much for your response. One more question. What value of
> corelation is acceptable/publishable?
>

A correlation > 0.999 is probably an indication of duplicate parameters in
a model, but it's common to publish parameters (say, N and sigma2 or E0 and
R) that are correlated by more than 0.9.   The correlation simply measures
the amount by which a parameters best-fit value would change if another
parameter was changed away from its best-fit value.   The uncertainties
take these correlations into account.


> also having a correlation number means the fit is not finished and I
> should change the values of variable that are correlated? is that so?
>

No.  The fit is (or "can be") finished.  The reported best-fit values are
really the best values found, and the reported uncertainties are those that
increase the best chi-square by reduced chi-square, taking into account the
correlation.    The correlation does not indicate a bad model or a bad fit,
it's just a consequence of the complex model and limited data for XAFS.

Hope that helps,

--Matt
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