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 Model comparison and Number of Parameters

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T O P I C    R E V I E W
SapereAude1490 Posted - 06/24/2022 : 07:24:20 AM
OriginPro 2018(64-bit)
Operating System: Windows 10

I have a question regarding the Fit Comparison of Models - the Bayesian and Akaike's Information Criterion Test.

I have a data set from which I'm deconvolving two or three lognormal distributions.

When I do the deconvolution and then compare the two models, I get the following:

Under the "Number of Parameters", why does it say 2 and 3 for the two compared models? Shouldn't it be 4 and 6 (2 mu's and sigma's, or 3 mu's and sigmas)? I'm a bit confused how does model comparison work with deconvolutions.

The two deconvolutions are shown below:

If anyone can explain how origin is doing this, I would be very grateful.
6   L A T E S T    R E P L I E S    (Newest First)
Sam Fang Posted - 06/27/2022 : 10:46:58 PM
Hi SapereAude1490,

I still can't reproduce your result.

I noticed that in the Fit Comparison report, Fit Reports are [Data]FitPeaks2x and [Data]FitPeaks3x. However [Data] book has no such sheets. So the comparison report may not use fit reports in current project?

OriginLab Technical Services
SapereAude1490 Posted - 06/27/2022 : 05:48:25 AM
Dear Sam,

Thanks for the quick reply. Here's the file:
Sam Fang Posted - 06/27/2022 : 05:29:02 AM
Hi SapereAude1490,

I can't reproduce your problem for number of parameters in Origin.

Can you send your project file to us? We can check it.


OriginLab Technical Services
SapereAude1490 Posted - 06/27/2022 : 04:42:12 AM
Hello Sam,

Thanks for your response. I didn't know K was number of parameters + 1. Thanks.

I tried doing the deconvolution again and not fixing any of the parameters (I did give it custom starting positions).

I got the exact same result as before. Is it working correctly with reporting of 2 and 3 parameters?

I also tried to change the K to K+1 in matlab and it does produce the same results now.

Sam Fang Posted - 06/27/2022 : 02:29:17 AM
Hi SapereAude1490,

Did you fix parameters in your fitting? Note that fixed parameters are not counted in K.

K is not the number of parameters, but the number of parameters plus 1. In your matlab example K=3.

OriginLab Technical Services
SapereAude1490 Posted - 06/24/2022 : 08:56:46 AM
So after digging a bit more, I found that origin is doing this:

But, if I try to do it manually (in MATLAB), I get different results for the AIC:

Why is there a difference between the AIC results in origin and matlab? Is it a rounding thing?

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