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Re: Very small P-Value for ETABAR

From: Nick Holford <n.holford>
Date: Sat, 15 Nov 2008 09:33:40 +1300

Jakob, Mats,

Thanks very much for your careful explanations of how asymmetric EBE
distributions can arise. That is very helpful for my understanding.

Xia,

I am intrigued by your suggestion for how to estimate and account for
the bias in the mean of the EBE distribution.

In the usual ETA on EPS model I might write:

; SD of residual error for mixed proportional and additive random effects
PROP=THETA(1)*F
ADD=THETA(2)
SD=SQRT(PROP*PROP + ADD*ADD)
Y=F + EPS(1)*SD*EXP(ETA(1))

where EPS(1) is distributed mean zero, variance 1 FIXED
and ETA(1) is the between subject random effect for residual error

You seem to be suggesting:
ETABAR=THETA(3)
Y=F + EPS(1)*SD*EXP(ETA(1)) * ETABAR*EXP(ETA(2))

It seems to me that the variance of ETA(1) will be confounded with the
variance of ETA(2). Would you please explain more clearly (with an
explicit NM-TRAN code fragment if possible) what you are suggesting?

Best wishes,

Nick

Xia Li wrote:
> Hi Jakob,
> Thank you very much for the information adding an "eta on epsilon". This is
> what I did in my research and I am glad to see people in Pharmacometrics is
> using it.
>
> And in Bayesian analysis, adding one more stage for ETA, i.e
> ETA=ETABAR*exp(eta2), eta2~N(0,omega2) will allow the deviation from zero
> and shrinkage of ETA.
>
> Again, thanks all for your input.:)
>
> Best Regards,
> Xia
>
> Xia Li
> Mathematical Science Department
> University of Cincinnati
>

--
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 Fri Nov 14 2008 - 15:33:40 EST

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