[Ifeffit] What confidence limit is implied in the error bars forleast-squares fitting in Athena

[Don R Baker]

Hi Shelly,

I am very interested in Andrew's question too, but I am to ignorant to
fully understand your response.  Could you please provide some more
detail?  For example, when you state "a large source of uncertainty can
come from the representation of the standards in matching the species in
the sample." do you mean that heterogeneities (as Bruce mentioned in his
email) in the standards are propagated into the fits of the unknowns?
Or instead do you mean that an inappropriate choice of standards can
create unreliability in the fit?  I would appreciate any details you can
add to your repsonse.

Thanks,

Don

On Thu, 2008-02-10 at 14:22 -0700, Kelly, Shelly wrote:
> Hi Andrew,
> 
>  
> 
> If you are fitting XANES spectra with standards, a large source of
> uncertainty can come from the representation of the standards in
> matching the species in the sample.
> 
>  
> 
> Shelly
> 
>  
> 
> 
> ______________________________________________________________________
> 
> From: ifeffit-bounces at millenia.cars.aps.anl.gov
> [mailto:ifeffit-bounces at millenia.cars.aps.anl.gov] On Behalf Of Andrew
> Sent: Thursday, October 02, 2008 3:49 PM
> To: ifeffit at millenia.cars.aps.anl.gov
> Subject: [Ifeffit] What confidence limit is implied in the error bars
> forleast-squares fitting in Athena
> 
>  
> 
> Hi everyone,
> 
>  
> 
> I’m fitting data with the least-squares method in Athena and am not
> sure what the error bars correspond to. What I mean, are these 95%
> confidence limits, or is it some other statistical way for error
> analysis?  If Athena says the weight of one phase is 0.049 (0.003),
> what confidence are in the 0.003 error bar reported by Athena?
> 
>  
> 
> (I have done a PCA of the XANES, and XRDs of the samples and am pretty
> confident in the phases that I’m fitting).
> 
>  
> 
> I greatly appreciate the help!
> 
>  
> 
> Andrew Campos
> 
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-- 
Melting rocks today for a better tomorrow . . .
Don R. Baker, Professor of Geochemistry, Earth and Planetary Sciences,
McGill University, Montreal, QC CANADA  phone: 1-514-398-7485