RE: Decrease in OFV with a fixed effect

From: "Mats Karlsson" mats.karlsson@farmbio.uu.se Subject: RE: [NMusers] Decrease in OFV with a fixed effect Date: Mon, August 23, 2004 10:12 am Hi Pete, The fact that you get an estimate of 10-4 for V1 variance, may be because variance is truly small (in which case adding covariate should not improve OFV), or because it is downwards biased due to model misspecification (e.g. through a diagonal omega structure). In the latter case, you can well expect an improvement in OFV if you add a true covariate (and maybe if you add a false one too it is difficult to know what can happen in misspecified models). 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