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RE: PARAMETER ESTIMATE IS NEAR ITS BOUNDARY with NONMEM v6

From: Fidler,Matt,FORT WORTH,R&D <Matt.Fidler>
Date: Fri, 25 Sep 2009 09:21:21 -0500

Durairaj,

My comments are as follows:

a) Is there any option to overcome this issue without suppressing the =
message as suggested earlier?

In my experience, changing initial estimates to estimates nearer the =
final estimate may cause this problem to disappear.

Also changing the units on your clearance, volume of distribution, etc., =
can cause this problem to disappear.

b) What causes the above problem? Do I need to avoid specifying any =
boundary for the thetas?

Your scaled parameter estimate is near the boundary of what was =
specified. When you expect the estimate or large to be small, this =
problem can occur.

c) What does this message indicate? a poor selection of model? poor =
initial estimates? narrow boundary? or any correlation issues with the =
estimates?

This message indicates that one of your parameters is either too small =
or too large, which sometimes may be taken care of with changing initial =
estimates. The rest of the questions are more easily answered in =
context of your model, what is expected.

Matt.

-----Original Message-----
From: owner-nmusers
On Behalf Of Durairaj Chandrasekar
Sent: Thursday, September 24, 2009 3:19 PM
To: nmusers
Subject: [NMusers] PARAMETER ESTIMATE IS NEAR ITS BOUNDARY with NONMEM =
v6

Dear group,

Recently I was running a sparse sampling animal data (one data per =
animal) using NONMEM v6 & WFN and ran into this trouble:

"PARAMETER ESTIMATE IS NEAR ITS BOUNDARY
 THIS MUST BE ADDRESSED BEFORE THE COVARIANCE STEP CAN BE IMPLEMENTED".

I searched the forum for any solution and found the message from Mark =
Sale (Next Level Solutions).

My question: a) Is there any option to overcome this issue without =
suppressing the message as suggested earlier?
b) What causes the above problem? Do I need to avoid specifying any =
boundary for the thetas?
c) What does this message indicate? a poor selection of model? poor =
initial estimates? narrow boundary? or any correlation issues with the =
estimates?

I highly appreciate your input. Thanks in advance

Regards,
Chandra Durairaj,
Post-doctoral Fellow,
Univ of Colorado Denver


      


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Thank you.
Received on Fri Sep 25 2009 - 10:21:21 EDT

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