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PS Your computer clock seems to be more than 2 years out of date.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: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On
Behalf Of Johan Wallin
Sent: Wednesday, October 15, 2008 9:17 AM
To: nmusers@globomaxnm.com
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: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On
Behalf Of Denney, William S.
Sent: den 15 oktober 2008 14:39
To: nmusers@globomaxnm.com
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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