[Ifeffit] S02

Bruce Ravel bravel at anl.gov
Thu Oct 20 13:09:43 CDT 2005


On Thursday 20 October 2005 12:03, Juan Antonio Maciá Agulló wrote:
> Thank you very much Bruce for your explanation. As you have commented, I
> have high correlations between S02 and sigma^2, I can not eliminate them by
> changing kw, so... what can I do?

The answer might very well be that you have to live with it.  These
correlations will be reflected in the size of the uncertainty.

In many cases it is possible to change some kind of extrinsic
parameter and invoke some knowledge of how your parameters change when
thatr extrinsic parameter is changed.

An example of an extrinsic parameter is temperature.  We presume that
S02 is constant in temperature and that sigma^2 behaves like a
single-frequency oscillator with temperature.  If you are able to make
a sequence of measurements as a function of temperature, the
variations in the data combined with your understanding of how the
data should behave can be very useful in determining parameters with
more confidence.

Of course, there are many situations where it is not possible to take
measurements as a function of temperature (or presure or whatever).
In that case we have to do the best we can and acknowledge that there
is some systematic uncertainty in the system.  In that case, one must
be honest about the uncertainties when reporting results.

B

-- 
 Bruce Ravel  ---------------------------------------------- bravel at anl.gov

 Molecular Environmental Science Group, Building 203, Room E-165
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