Dear Samer,
I parameterized the model by CL, Q , V1 and V2 and by CL,Q, V1 and Vss
respectively. Correlation was not included at this time. The latter model
lead to a lower OFV (~5), which is why I choosed to go on with this
paramerization. Both models show correlation between the volumes V1 and V2
or V1 and VSS respectively in the scatter plot matrix of random effect,
when no correlation is included into the model. So is it better to go with
parameterization CL, Q, V1 and V2, even though I have correlation in both
cases?
Hauke
Am 03.08.2009, 18:42 Uhr, schrieb Samer Mouksassi
<[email protected]>:
What do you mean by much better ?
OFV ? BSV % etc..
Can you please in clude a brief comparison on both cases
Samer
-----Original Message-----
From: [email protected] [mailto:[email protected]]
On Behalf Of Hauke Rühs
Sent: 2009-08-03 12:06
To: [email protected]
Subject: Re: [NMusers] OMEGA-Block
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
<[email protected]>:
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
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Clin. Pharmacology and DMPK
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Tel: +44 1509 644035
[email protected]
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-----Original Message-----
From: [email protected]
[mailto:[email protected]]on Behalf Of Hauke Rühs
Sent: 03 August 2009 15:07
To: [email protected]
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
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