RE: $PRIOR with normal for OMEGA?
Hi
To add on Martin’s suggestion, one item to think of when using theta for
estimating the variances of eta is to use log scaled STD as your model
parameter, so instead of THETA*ETA (with OMEGA fixed) use exp(THETA)*ETA.
This way you would assume a log-normal prior for the standard deviation of ETA
which is more reasonable.
Moreover the log-normal is quite close to the gamma distribution which I
believe is the (univariate) distribution of diagonal elements of the inverse
Wishart.
Kind Regards
Magnus Åstrand
Principal Clinical Pharmacometrician, Ph.D.
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From: [email protected] [mailto:[email protected]] On
Behalf Of Martin Bergstrand
Sent: den 11 november 2016 08:32
To: Mark Sale <[email protected]>
Cc: [email protected]
Subject: Re: [NMusers] $PRIOR with normal for OMEGA?
Hi Mark,
Not sure about this but how about estimating THETAS scaling fix OMEGAs (e.g. CL
= THETA(1)*EXP(THETA(2)*ETA(1)) ; $OMEGA 1 fix)? Then you can implement the
prior in the same way for random effect parameters as you do for fixed effect
parameters.
Ps. Probably not be compatible with MU-parameterization.
Best regards,
Martin Bergstrand, Ph.D.
Senior Consultant
Pharmetheus AB
+46(0)709 994 396<tel:+46709%C2%A0994%20396>
[email protected]<mailto:[email protected]>
http://www.pharmetheus.com/
+46(0)18 513 328<tel:+4618%20513%20328>
U-A Science Park, Dag Hammarskjölds v. 52b
752 37 Uppsala, Sweden
Skickat från min iPhone
11 nov. 2016 kl. 04:57 skrev Mark Sale
<[email protected]<mailto:[email protected]>>:
Is it possible to use a normal prior for OMEGA? The default is inverse Wishart,
but I'd be interested in using Normal (insuring that it is positive definite)
Any ideas?
thanks
Mark Sale M.D.
Vice President, Modeling and Simulation
Nuventra Pharma Sciences, Inc.
2525 Meridian Parkway, Suite 280
Durham, NC 27713
Phone (919)-973-0383
[email protected]<[email protected]>
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