Re: OMEGA selection

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/ [email protected] /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 [email protected] 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