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From: Grevel, Joachim <Joachim.Grevel>
Date: Mon, 3 Aug 2009 15:37:46 +0100

Hello Hauke,

as always for these specific questions you need to provide us with the =
relevant portions of your control stream and of your output.

Thanks for participating,

AstraZeneca R&D Charnwood
Clin. Pharmacology and DMPK
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Loughborough, LE11 5RH
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-----Original Message-----
From: owner-nmusers
Sent: 03 August 2009 15:07
To: nmusers
Subject: [NMusers] OMEGA-Block

Dear NMusers,

modelling a 2-compartmet model parameterized by CL, V1, VSS and Q, I got =
to a problem with which I don’t know how to deal with: After =
choosing my
structural and statistic model (combined residual error model) I =
the covariance matrix by including an OMEGA-BLOCK(4), which reduced the =

OFV by 15. The correlations between the parameters were all estimated to =
be minor (< 0.8). But when I model with a BLOCK(2) on VSS and V1, which =
would expect to be positively correlated, the correlation is estimated =
be -0.99. Additionally, the inclusion of BLOCK(2) does not significantly =
improve the OFV.
So does it, after all, still make sense to include the BLOCK(2)?
Generally, at which step of model-building would you recommend to test =
parameter correlation?

Thanking you in advance,


Hauke Rühs

Pharmazeutisches Institut
- Klinische Pharmazie -
An der Immenburg 4

53121 Bonn

Tel: + 49-(0)228 73-5781
Fax: + 49-(0)228 73-9757

Received on Mon Aug 03 2009 - 10:37:46 EDT

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