NONMEM Users Network Archive

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Re: VPC with Mixture Model

From: Leonid Gibiansky <LGibiansky>
Date: Tue, 14 Apr 2009 15:06:06 -0400

Hi Mats,

Could you elaborate why you would not stratify based on the
subpopulations? It seems perfectly reasonable for me to simulate from
the model (including random assignment of subpopulations), and then
compare "apples to apples": observed subpopulation versus simulated
subpopulations. In your example of 5% poor metabolizers, I would plot
observed poor metabolizers (as assigned by the model) versus simulated
poor metabolizers (as simulated from the model). Indeed, poor
metabolizers assignment would be defined by the model, so this VPC will
be conditioned on the model posthoc EST prediction, but the remaining
parts of the model would be tested by this procedure. If the model is
good, VPC should provide good results. It is unclear to me how sensitive
this procedure is to model misspecification (in general, I think VPC is
less sensitive to model misspecification than other model diagnostics)

Thanks
Leonid

--------------------------------------
Leonid Gibiansky, Ph.D.
President, QuantPharm LLC
web: www.quantpharm.com
e-mail: LGibiansky at quantpharm.com
tel: (301) 767 5566




Mats Karlsson wrote:
> Dear Satyendra,
>
>
>
> Interesting question. I don’t think there is much written about this,
> but I may be wrong. What I would not do is to try to stratify based on
> estimated subpopulation allocation (“EST”). Rather I would use the same
> VPCs as if there had been no mixture model. Possibly what you could do
> is be more careful in your choice of prediction intervals to display.
> For example, if you have a subpopulation of poor metabolizers of about
> 5%, displaying only median and interquartile range PIs may not be a good
> idea.
>
>
>
> Best regards,
>
> Mats
>
>
>
> Mats Karlsson, PhD
>
> Professor of Pharmacometrics
>
> Dept of Pharmaceutical Biosciences
>
> Uppsala University
>
> Box 591
>
> 751 24 Uppsala Sweden
>
> phone: +46 18 4714105
>
> fax: +46 18 471 4003
>
>
>
> *From:* owner-nmusers
> [mailto:owner-nmusers
> *Sent:* Tuesday, April 14, 2009 6:50 PM
> *To:* nmusers
> *Subject:* [NMusers] VPC with Mixture Model
>
>
>
> Dear all,
>
> I have a Mixture Model with 2 subpopulation. Now I want to check its
> prediction. One way to see this is a Visual Predictive Check. My
> question is, How to perform visual predictive check with mixture model?
>
> I will be thankful for your suggestion and references.
>
>
>
> Best regards
>
>
>
> Satyendra Suryawanshi, PhD
>
> University of Tennessee Health Science Center
>
>
>
Received on Tue Apr 14 2009 - 15:06:06 EDT

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