Re: covariance step

Varsha, The message you show below is not an error. It is just a warning. Errors and warnings are very different. An error will cause NONMEM to stop and usually give you some clue to the problem. A warning does not mean there is a problem -- it is just a clue that there may be a problem and its up to the user to do some thinking. There may be nothing for you to worry about. As others have pointed out the message you show often turns up in NONMEM VI because the OMEGA estimate is close to 0. Many people found this message irritating when NONMEM VI first came out so in later versions you can tell NONMEM (via NM-TRAN) abbreviated code) not to issue this kind of warning. In the end it is up to you to make a decision about whether the model is reasonable or not. NONMEM has no idea. Indeed it has been discussed many times on this list that there is typically no difference between models which NONMEM reports as successful versus those that NONMEM terminates because of rounding errors. You have to learn to take responsibility for modelling decisions and not pay too much attention to the messages that NONMEM issues. Nick Varsha Mehta wrote: > Dear NONMEM users: > > I have a data set for 30 infants where I am running a 2 COMPT PK model. I got > the following error message for the covariance step. I need some help with > trying to fix this error. Any suggestions? should I increase the upper > boundries of initial estimates? > > MINIMIZATION SUCCESSFUL > NO. OF FUNCTION EVALUATIONS USED: 289 > NO. OF SIG. DIGITS IN FINAL EST.: 3.0 > 0PARAMETER ESTIMATE IS NEAR ITS BOUNDARY > THIS MUST BE ADDRESSED BEFORE THE COVARIANCE STEP CAN BE IMPLEMENTED > > any help is appreciated. > Thanks > > Varsha Mehta, MS(CRDSA), Pharm.D., FCCP > Clinical Associate Professor > Pharmacy, Pediatrics and Communicable Diseases > Clinical Pharmacist Neonatal Critical Care > University of Michigan > (O) 734-936-8985 > (F) 734-936-6946 > [email protected] > > ********************************************************** > Electronic Mail is not secure, may not be read every day, and should not be > used for urgent or sensitive issues -- Nick Holford, Professor Clinical Pharmacology 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 20 2009) http://www.fmhs.auckland.ac.nz/sms/pharmacology/holford