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Re: Model building

From: Indranil Bhattacharya <ibhattacharya>
Date: Fri, 4 Dec 2009 12:06:08 -0500

Thanks Joachim, that is what I thought. I wanted to be sure that I invest
time building the right model and not just some model which works
(converges) but is biased.

Neil

On Fri, Dec 4, 2009 at 3:31 AM, Grevel, Joachim <
Joachim.Grevel

> 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 bas=
ic
> 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
>
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> *From:* owner-nmusers
m]
> *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 WRE=
S
> 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 n=
ot
> 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 ha=
ve
> meaning even when the minimization terminates.
>
>
>
> Regards
>
>
>
> Neil
>
> --
> Indranil Bhattacharya
>
>


--
Indranil Bhattacharya

Received on Fri Dec 04 2009 - 12:06:08 EST

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