Non-physiological parameters at lowest OBJ

From: Justin Wilkins <jwilkins@uctgsh1.uct.ac.za> Subject: [NMusers] Non-physiological parameters at lowest OBJ Date: 8/5/2003 6:16 AM Hi all, Just as a general discussion point... Our group is faced with a situation which goes as follows: In a given one-compartment (ADVAN2) model, one set of initial estimates minimizes successfully with parameter estimates that are in broad agreement with prior published information. However, another set of initial estimates minimizes successfully with an objective function 200 units lower, but with physiologically impossible parameter estimates. Both sets completed the covariance step successfully as well. Any ideas on the best way to deal with this, and its potential causes? The first case appears to be reaching a local minimum, but its results are believable, whereas the second's are obviously not correct. The only solution appears to be constrain initial estimates to physiological limits. Both analyses currently underway at our site have independently run into this problem. Best regards, Justin Wilkins Division of Pharmacology Faculty of Health Sciences University of Cape Town