RE: BOV
From: "Mats Karlsson" mats.karlsson@farmbio.uu.se
Subject: RE: [NMusers] BOV
Date: Thu, September 23, 2004 2:05 pm
Hi Ken,
Just on a minor point in your email - I wasn't referring to
autocorrelation (which may not harm NONMEM parameter estimates [see JPB
1995, 23(6): 651-672], but which I do believe is likely to cause
problems with likelihood ratio test). I was referring to when residual
error magnitude varying in time [JPB 1998, 16:207-246], which can often
be seen, when looked for. For describing data following oral
administration, often a heteroscedatic error model such as Y=F+F*EPS(1)
is used. It assumes, often incorrectly, that the error magnitude is the
same for comparable concentrations during the ascending and descending
portions of the curve. However, in general, error magnitude is usually
considerably higher during the ascending portion as the absorption
process is more variable and often associated with higher model
misspecification.
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