NONMEM Users Network Archive

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RE: PPC

From: Bachman, William <William.Bachman>
Date: Thu, 31 Jul 2008 09:02:11 -0400

Your bootstrap runs may terminate because of "parameter estimates near
to the boundary" due to a new feature in NONMEM VI, the "default
boundary test". See the help manual entry for $ESTIMATION:

 THETABOUNDTEST, OMEGABOUNDTEST, SIGMABOUNDTEST
|
      With NONMEM VI, the estimation step sometimes terminates with the
|
      message
|
      PARAMETER ESTIMATE IS NEAR ITS DEFAULT BOUNDARY.
|
      These options request that the "default boundary test" be per-
|
      formed for THETA, OMEGA, and SIGMA, respectively. THETABOUNDTEST
|
      may also be coded TBT or TBOUNDTEST; OMEGABOUNDTEST may also be
|
      coded OBT or OBOUNDTEST; SIGMABOUNDTEST may also be coded SBT or
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      SBOUNDTEST. These options are the defaults.
|

 NOTHETABOUNDTEST, NOOMEGABOUNDTEST, NOSIGMABOUNDTEST
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      Instructs NONMEM to omit the "default boundary test" for this
|
      type of variable, i.e., to behave like NONMEM V in this regard.
|
      Any option listed above may be preceded by "NO". The THETA,
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      OMEGA, and SIGMA choices are independent of each other. E.g., it
|
      is possible to specify NOOBT (to prevent the "default OMEGA boun-
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      dary test") and permit both the "default THETA boundary test" and
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      "default SIGMA boundary test".
|

Try turning turning off "default boundary test".

William J. Bachman, Ph.D.
Director, Pharmacometrics R&D
Icon Development Solutions
6031 University Blvd., Suite 300
Ellicott City, MD 21043
Office 410-696-3002
Cell 301-467-8635

________________________________

From: owner-nmusers
On Behalf Of andreas lindauer
Sent: Thursday, July 31, 2008 7:27 AM
To: nmusers
Subject: RE: [NMusers] PPC



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

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Received on Thu Jul 31 2008 - 09:02:11 EDT

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