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Re: More Levels of Random Effects

From: Nick Holford <n.holford>
Date: Fri, 17 Oct 2008 13:02:49 +1300

Xia,

There is no requirement to use the SAME option. However, it is a
reasonable model for IOV that it has the same variability on each occasion.

If you dont use the SAME option then you just need to estimate an extra
OMEGA parameter for each occasion you dont use SAME. You can test if the
SAME assumption is supported by your data or not by comparing models
with and without SAME.

Nick

PS Your computer clock seems to be more than 2 years out of date. Your
email claimed it was sent in 17 Jan 2006.

Xia Li wrote:
> Dear All,
> Do we have to assume the variability between all occasions are the same when
> we estimate IOV? What will happen if I don't use the 'same' constrain in the
> $OMEGA BLOCK statement? Any input will be appreciated.
>
> Best,
>
> Xia Li
>
> -----Original Message-----
> From: owner-nmusers
> Behalf Of Johan Wallin
> Sent: Wednesday, October 15, 2008 9:17 AM
> To: nmusers
> Subject: RE: [NMusers] More Levels of Random Effects
>
> Bill,
> Is it really an eta you want, or is this rather solved by different error
> models for the different machines?
>
> If still want etas, one way would be to model in the same way as IOV. In the
> case of intermachine-variability you would have to assume the variability
> between all machines are the same...
> Or would you rather assume interindividual variability is different with
> different machine, and you then would want one eta for TH(X) for every
> machine...? It depends on what you mean by different slope every day,
> regarding on what your experiments like, but calibration differences should
> perhaps be taken care of by looking into your error model, eta on epsilon
> for starters...
>
> Without knowing your structure of data, a short example of IOV-like
> variability would be:
>
> MA1=0
> MA2=0
> IF(MACH=1)MA1=1
> IF(MACH=2)MA2=1
> ;Intermachine variability:
> ETAM = MA1*ETA(Y)+MA2*ETA(Z)
>
> PAR= TH(X) *EXP(ETA(X)+ETAM)
>
> $OMEGA
> value1
> $OMEGA BLOCK(1) value2
> $OMEGA BLOCK(1) same
>
> /Johan
>
>
>
> _________________________________________
> Johan Wallin, M.Sci./Ph.D.-student
> Pharmacometrics Group
> Div. of Pharmacokinetics and Drug therapy
> Uppsala University
> _________________________________________
>
>
> -----Original Message-----
> From: owner-nmusers
> Behalf Of Denney, William S.
> Sent: den 15 oktober 2008 14:39
> To: nmusers
> Subject: [NMusers] More Levels of Random Effects
>
> Hello,
>
> I'm trying to build a model where I need to have ETAs generated on
> separately for the ID and another variable (MACH). What I have is a PD
> experiment that was run on several different machines (MACH). Each
> machine appears to have a different slope per day and a different
> calibration. I still need to keep some ETAs on the ID column, so I
> can't just assign MACH=ID.
>
> I've heard that there are ways to do similar to this, but I have been
> unable to find examples of how to set etas to key off of different
> columns.
>
> Thanks,
>
> Bill
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--
Nick Holford, Dept Pharmacology & Clinical Pharmacology
University of Auckland, 85 Park Rd, Private Bag 92019, Auckland, New Zealand
n.holford
http://www.fmhs.auckland.ac.nz/sms/pharmacology/holford
Received on Thu Oct 16 2008 - 20:02:49 EDT

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