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
[EMAIL PROTECTED] tel:+64(9)923-6730 fax:+64(9)373-7090
http://www.fmhs.auckland.ac.nz/sms/pharmacology/holford
