Re: Parameterization!!!

From: Mats Karlsson <Mats.Karlsson@farmbio.uu.se> Subject: Re: Parameterization!!! Date: Thu, 10 May 2001 17:14:36 +0200 Dear all, Just as another possibility regarding parametrisation. If you look for covariate-parameter relations using posthoc etas (or parameters), it might be useful to look at not only the eta for CL and that for V (if those are the parameters we are interested in) but also try to isolate the covariance and see if that correlates with any covariate (that is can any covariate explain the correlation per se). One way of doing that is to use models like CL=THETA(1)*EXP(ETA(1)+ETA(3)) V=THETA(2)*EXP(ETA(2)+ETA(3)) and $OMEGA DIAG(3) and then look at covariate models for ETA(3) (representing the covariance) as well as the ETA(1), ETA(2) (uncorrelated variability in CL and V) and the sums ETA(1)+ETA(3) and ETA(2)+ETA(3). (I know this is not an entirely general model, but one that most often would be biologically reasonable for CL and V). Best regards, Mats -- Mats Karlsson, PhD Professor of Pharmacometrics Div. of Pharmacokinetics and Drug Therapy Dept. of Pharmaceutical Biosciences Faculty of Pharmacy Uppsala University Box 591 SE-751 24 Uppsala Sweden phone +46 18 471 4105 fax +46 18 471 4003 mats.karlsson@farmbio.uu.se