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RE: Model building

From: Grevel, Joachim <Joachim.Grevel>
Date: Fri, 4 Dec 2009 08:31:18 -0000

Hi Neil,

 

You ask:

 

"So my question is whether the fits, RES, WRES plots and the ofv values
have meaning even when the minimization terminates"

 

The answer: you bet they matter! Residual plots are the most informative
output NONMEM gives you. They should guide you when you determine the
basic structure of your model that is supported by the data. Successful
termination, covariance step, standard errors, Eigen values, messages,
warnings... are just icing on the cake vis-a-vis the residual plots.

 

These are my two pennies worth of advice,

 

Joachim

 

 

Joachim Grevel

Senior Pharmacometrician

_____________________________________________________________________

AstraZeneca R&D Charnwood

Clinical Pharmacology & DMPK, Charnwood

Bakewell Road, Loughborough, Leics., LE11 5RH, England

Tel +44 (0) 1509 644035 Fax +44 (0) 1509 645576 Mobile +44 (0) 7920
285905

joachim.grevel

 

 P Please consider the environment before printing this e-mail

 

 

 

From: owner-nmusers
On Behalf Of Indranil Bhattacharya
Sent: 03 December 2009 15:41
To: nmusers
Subject: [NMusers] Model building

 

Hi, I am in the process of developing a PK/PD model and have a naive
question regarding model building.

I currently do not have all the PD data and more data would be available
in the future. For the current data set, I have tried models say A to D.


Now model A (cell kill) and B (cell kill +transduction) converges using
FOCE (no CV% but I am willing to live with that) but from the RES and
WRES plots we can clearly see that there is some bias. The fit is OK but
not great. The ofv values are around 400.

Now models B (cell cycle specific kill), C (cell + precursor cell kill
+transduction) and D (cell cycle specific + indirect response model) do
not converge using FO or FOCE methods but when I look at the fits from
the terminated runs, the fits are much better than those obtained with
Model A, and there seems very little bias. Also the ofv values are
between 160-250.

 

So my question is whether the fits, RES, WRES plots and the ofv values
have meaning even when the minimization terminates.

 

Regards

 

Neil

--
Indranil Bhattacharya


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Received on Fri Dec 04 2009 - 03:31:18 EST

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