NONMEM Users Network Archive

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Re: PPC

From: Nick Holford <n.holford>
Date: Fri, 01 Aug 2008 12:51:33 +1200

Andreas,

If this happens to 10% of your runs then its pretty strong evidence that
the uncertainty in the OMEGA estimate would lead to a 95% CI very close
to zero. I would consider simplifying the model and fixing that OMEGA to
0. Then evaluate the model for its intended purpose and decide if this
simplification had any impact on the use of the model.

With NMVI you can now choose to turn off this warning which may allow
you convince yoursefl more clearly that the lower bound of the
confidence interval is close to zero.

Nick

andreas lindauer wrote:
>
> Hello NMUSERS,
>
> Let me just add one more thought on the bootstrap discussion.
> Sometimes when doing a bootstrap it happens that the runs terminate
> because of parameter estimates near to the boundary (e.g. values for
> OMEGA close to 0). When this happens in a considerable number of runs,
> lets say in 10% of the runs, how would you then calculate the CI for
> that parameter? Because the bootstrap parameter distribution derived
> from all runs - irrespective of their termination status would then
> be bimodal with one mode close to the boundary.
>
> Best regards, Andreas.
>
> ____________________________
>
> Andreas Lindauer
>
> University of Bonn
>
> Department of Clinical Pharmacy
>
> An der Immenburg 4
>
> D-53121 Bonn
>
> phone:+49 228 73 5781
>
> fax: +49 228 73 9757
>

--
Nick Holford, Dept Pharmacology & Clinical Pharmacology
University of Auckland, 85 Park Rd, Private Bag 92019, Auckland, New Zealand
n.holford
http://www.fmhs.auckland.ac.nz/sms/pharmacology/holford

Received on Thu Jul 31 2008 - 20:51:33 EDT

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