Hi all, Scott answered my question about consistency but now I have a new doubt. I have two fits (one in k1 and other in k3 weights) with fitted parameters that have uncertainty ranges overlaped, then... in principle, they are consitent, right? But the fit in k1 weight have a R-factor too high (0.06) and therefore is not a good fit. So I do not know if I can say that they are consistent even so. Thank you very much Best regards, JA
I read in Artemis manual that a good fit must be consistent for different k-weights. When two fits (one with k1 and other with k3) are consistent? I mean, which is maximum allowed difference, 1%, 5%...between these two fits?
Ideally, the fitted parameters should have uncertainty ranges that overlap. For example, one bond length might be 2.03 +/- 0.04 angstroms, and the equivalent bond length using a different k-weight might be 2.09 +/- 0.03 angstroms.
Hi Juan, They're consistent. The higher r-factor on the kwt-1 data might be a clue about how reliable part of your data range is...since it's the kwt-1 that's higher, it may be that the low end of the k-range is not being fit very well (look at the k-space and q-space fits to help confirm this). That could be just because of glitchy data, iffy background subtraction, or that your model doesn't do as well with low-Z scatterers like oxygen as it does with the higher-Z contributions (the low-Z scatterers have most of their contributions at low k). Aside from looking at the k- and q-space fits, I'd try increasing kmin and see if that improves the fit. If it does, you might want to do it on the kwt-3 fit too, because that would suggest you're not fitting that low-k data very well, and the problem is just less emphasized with kwt-3. Of course it would be even better to find the source of the problem and address it. Having said that, I should emphasize that these are non-linear fits. Sometimes it's hard to come up with a simple explanation for why one fit is closer than another. Nevertheless, your fits are consistent. They're not equally "good"...but that's a different statement. In your situation, I would be comfortable publishing the kwt-3 fit and saying that other kwts gave consistent results. I would be more comfortable if I could figure out what was troubling the kwt-1 fit, though...especially if I had a mix of scatterers with substantially different atomic number (like transition metals with oxygens). --Scott Calvin Sarah Lawrence College At 08:03 AM 9/28/2006, you wrote:
Hi all,
Scott answered my question about consistency but now I have a new doubt. I have two fits (one in k1 and other in k3 weights) with fitted parameters that have uncertainty ranges overlaped, then... in principle, they are consitent, right? But the fit in k1 weight have a R-factor too high (0.06) and therefore is not a good fit. So I do not know if I can say that they are consistent even so.
Hi Scott, Thanks a lot, you are a good fortune-teller. I have low-Z scatterers (oxygen) and high-Z scatteres (Pt). Best regards, JA Scott Calvin ha escrito:
Hi Juan,
They're consistent. The higher r-factor on the kwt-1 data might be a clue about how reliable part of your data range is...since it's the kwt-1 that's higher, it may be that the low end of the k-range is not being fit very well (look at the k-space and q-space fits to help confirm this). That could be just because of glitchy data, iffy background subtraction, or that your model doesn't do as well with low-Z scatterers like oxygen as it does with the higher-Z contributions (the low-Z scatterers have most of their contributions at low k). Aside from looking at the k- and q-space fits, I'd try increasing kmin and see if that improves the fit. If it does, you might want to do it on the kwt-3 fit too, because that would suggest you're not fitting that low-k data very well, and the problem is just less emphasized with kwt-3. Of course it would be even better to find the source of the problem and address it.
Having said that, I should emphasize that these are non-linear fits. Sometimes it's hard to come up with a simple explanation for why one fit is closer than another.
Nevertheless, your fits are consistent. They're not equally "good"...but that's a different statement. In your situation, I would be comfortable publishing the kwt-3 fit and saying that other kwts gave consistent results. I would be more comfortable if I could figure out what was troubling the kwt-1 fit, though...especially if I had a mix of scatterers with substantially different atomic number (like transition metals with oxygens).
--Scott Calvin Sarah Lawrence College
At 08:03 AM 9/28/2006, you wrote:
Hi all,
Scott answered my question about consistency but now I have a new doubt. I have two fits (one in k1 and other in k3 weights) with fitted parameters that have uncertainty ranges overlaped, then... in principle, they are consitent, right? But the fit in k1 weight have a R-factor too high (0.06) and therefore is not a good fit. So I do not know if I can say that they are consistent even so.
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Hi all, Due to the great help obtained from this forum I decide to include it in the acknowledgements of the revised paper. Maybe you are not aware of this help but you solve my doubts. I think it is the least I can do (I can not include all of you because you are too many, : )). And now, I would like to ask the "manager" of this list how can I call it. Maybe, Mailing list of XAFS Analysis using Ifeffit? or just, Mailing List-Ifeffit? Other options... Thanks again Best regards, JA
participants (2)
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Juan Antonio Maciá Agulló -
Scott Calvin