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Re: OMEGA-Block

From: Leonid Gibiansky <LGibiansky>
Date: Mon, 03 Aug 2009 14:11:23 -0400

I guess, you can safely remove ETA4 on VSS from the model
Leonid
--------------------------------------
Leonid Gibiansky, Ph.D.
President, QuantPharm LLC
web: www.quantpharm.com
e-mail: LGibiansky at quantpharm.com
tel: (301) 767 5566




Hauke Rühs wrote:
>
> Dear NMusers,
>
> thank you for your responses. I parameterized the model by VSS, because
> the estimation of the parameter became much better, in terms of
> varability, compared to parameterization by V1 and V2.
> This is the excerpt from my control stream and output file:
>
>
> $PK
> CL = THETA(1) * EXP(ETA(1))
> Q = THETA(2) * EXP(ETA(2))
> V1 = THETA(3)* EXP(ETA(3))
> VSS = THETA(4) * EXP(ETA(4))
> V2=VSS-V1
>
> $OMEGA
> 0.1 ; OMCL
> 0.5 ;OMQ
> $OMEGA BLOCK(2)
> 0.05 ;OMV1
> 0.01 0.05 ;OMVSS
>
>
> OMEGA - COV MATRIX FOR RANDOM EFFECTS - ETAS ********
>
>
> ETA1 ETA2 ETA3 ETA4
>
> ETA1
> + 4.08E-02
>
> ETA2
> + 0.00E+00 4.56E-01
>
> ETA3
> + 0.00E+00 0.00E+00 2.62E-01
>
> ETA4
> + 0.00E+00 0.00E+00 -4.34E-02 7.20E-03
>
>
> Best regards
>
> Hauke
>
>
>
>
> Am 03.08.2009, 16:37 Uhr, schrieb Grevel, Joachim
> <Joachim.Grevel
>
>> 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,
>>
>> Joachim
>> _________________________________
>> AstraZeneca R&D Charnwood
>> Clin. Pharmacology and DMPK
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>> joachim.grevel
>>
>>
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>> -----Original Message-----
>> From: owner-nmusers
>> [mailto: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
>> estimated
>> 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 I
>> would expect to be positively correlated, the correlation is estimated to
>> 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
>> for
>> parameter correlation?
>>
>> Thanking you in advance,
>>
>> Hauke
>>
>> -----------------------------
>> Hauke Rühs
>>
>> Apotheker
>> Pharmazeutisches Institut
>> - Klinische Pharmazie -
>> An der Immenburg 4
>>
>> 53121 Bonn
>>
>> Tel: + 49-(0)228 73-5781
>> Fax: + 49-(0)228 73-9757
>>
>> www.klinische-pharmazie.info
>>
>>
>
Received on Mon Aug 03 2009 - 14:11:23 EDT

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