Author 
Topic 

SapereAude1490
Slovenia
4 Posts 
Posted  06/24/2022 : 07:24:20 AM

OriginPro 2018(64bit) 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. 

SapereAude1490
Slovenia
4 Posts 
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? 


Sam Fang
281 Posts 
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.
Sam OriginLab Technical Services 


SapereAude1490
Slovenia
4 Posts 
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
281 Posts 
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.
Thanks.
Sam OriginLab Technical Services 


SapereAude1490
Slovenia
4 Posts 

Sam Fang
281 Posts 
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?
Sam OriginLab Technical Services 



Topic 
