Ethan,
Do not pay any attention to whether or not the $COV step runs or even if
the run is 'SUCCESSFUL' to conclude anything about your model. Your
opinion is not supported experimentally e.g. see
http://www.mail-archive.com/nmusers@globomaxnm.com/msg00454.html for
discussion and references.
NONMEM has no idea if the parameters make sense or not and will happily
converge with models that are overparameterised. You cannot rely on a
failed $COV step or a MINIMIZATION TERMINATED message to conclude the
model is not a good one. You need to use your brains (NONMEM does not
have a brain) and your common sense to decide if your model makes sense
or is perhaps overparameterised.
Nick
Ethan Wu wrote:
Dear all,
I am fitting a PD response, and the equation goes like this:
total response = baseline+f(placebo response) +f(drug response)
first, I tried full omega block, and model was able to converge, but
$COV stop failed.
To me, this indicates that too many parameters in the model. The
structure model is rather simple one, so I think probably too many Etas.
I wonder is there a good principle of Eta reduction that I could
implement here. Any good reference?
--
Nick Holford, Dept Pharmacology & Clinical Pharmacology
University of Auckland, 85 Park Rd, Private Bag 92019, Auckland, New Zealand
n.holf...@auckland.ac.nz tel:+64(9)923-6730 fax:+64(9)373-7090
mobile: +33 64 271-6369 (Apr 6-Jul 17 2009)
http://www.fmhs.auckland.ac.nz/sms/pharmacology/holford
