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The following message was posted to: PharmPK
I have been trying to set weightage to assign larger weight to lower
concs. but unable to do so with Kinetica. The weight must be a direct
function of Y or Y^2. It cannot be entered as a reciprocal of the conc.
Does anybody have some way of working around this problem, e.g.
manipulating its coefficient sigma?
Lai-San Tham, PharmD
Department of Hematology-Oncology
National University Hospital, Singapore
[I'm not really familiar with Kinetica but my guess is that Y^2 means
weight = 1/Yvalue^2 where Y is the concentration - db]
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Dear Lai-San Tham:
Why do you want to weight your data that way? I know that is
commonly done, but the reasoning for it is not clear to me. Why not
weight it according to the reciprocal of its variance at each
concentration, according to its assay error polynomial? You might look
Jelliffe RW, Schumitzky A, Van Guilder M, Liu M, Hu L, Maire P, Gomis
P, Barbaut X, and Tahani B: Individualizing Drug Dosage Regimens: Roles
of Population Pharmacokinetic and Dynamic Models, Bayesian Fitting, and
Adaptive Control. Therapeutic Drug Monitoring, 15: 380-393, 1993.
Then, when you make your model, you can also estimate the
remaining environmental error. Go to our web site www.lapk.org, and
click on Teaching Topics, go to section 7, and look at material on the
assay error polynomial.
Very best regards,
Roger W. Jelliffe, M.D. Professor of Medicine,
Division of Geriatric Medicine,
Laboratory of Applied Pharmacokinetics,
USC Keck School of Medicine
2250 Alcazar St, Los Angeles CA 90033, USA
Phone (323)442-1300, fax (323)442-1302, email= jelliffe.at.usc.edu
Our web site= http://www.lapk.org
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