jmt3
☆

Australia,
2022-04-03 10:25
(356 d 09:14 ago)

Posting: # 22903
Views: 907

## IWRES and NPDE vs time/concentration plots interpretation [General Sta­tis­tics]

https://www.linkpicture.com/q/Model-1.png
https://www.linkpicture.com/q/Model-2.png
https://www.linkpicture.com/q/Model-3.png

Hello everyone,

I have a question with regards to the scatter plot of residual (especially IWRES and NPDE vs time/concentration). I have two different plots here simulating from two different structural models in NLME PopPk model (see attached Model 1 and Model 2 plots).

My understanding is that the scatter plot of residual tells you how much the predicted data deviates from the observed data. Based on these two plots (IWRES and NPDE of model 1 vs model 2), my understanding is that Model 1 is better than Model 2 only because the interpolation spline of Model 1 (the yellow line) lies on the horizontal y=0 line. In contrast, Model 2 has the trend line scattering unevenly on the horizontal line, and it even increasingly shows deviation when the time and the concentration are higher. Is my interpretation correct?

How about the plot from Model 3 (see attached)? I won't consider this model because all the data skewed towards right, and hence it is telling model misspecification? am I correct in this?

I hope this makes sense.

Thanks in advance
mittyri
★★

Russia,
2022-04-05 11:56
(354 d 07:43 ago)

@ jmt3
Posting: # 22909
Views: 659

## IWRES and NPDE vs time/concentration plots interpretation

Hi jmt3!

❝ I have two different plots here simulating from two different structural models in NLME PopPk model (see attached Model 1 and Model 2 plots).

I see you are using Monolix. Great, they did a lot of improvements last years.

❝ My understanding is that the scatter plot of residual tells you how much the predicted data deviates from the observed data.

More about this here

❝ Based on these two plots (IWRES and NPDE of model 1 vs model 2), my understanding is that Model 1 is better than Model 2 only because the interpolation spline of Model 1 (the yellow line) lies on the horizontal y=0 line. In contrast, Model 2 has the trend line scattering unevenly on the horizontal line, and it even increasingly shows deviation when the time and the concentration are higher. Is my interpretation correct?

Yes, that's correct. But please note that as Samer pointed out, Model 1 is still not good at the 2nd point

❝ How about the plot from Model 3 (see attached)? I won't consider this model because all the data skewed towards right, and hence it is telling model misspecification? am I correct in this?

yes, I think you are correct, but again, as Samer pointed out, more info is required. I don't think that BEBAC is a good place for NLME discussion, but you can try

Kind regards,
Mittyri
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