MIXTURE modeling

From: "Joern Loetsch" j.loetsch@em.uni-frankfurt.de Subject: [NMusers] MIXTURE modeling Date: Thu, 17 Nov 2005 11:29:13 +0100 Dear NONMEM users, I am working on a mixture model and would be grateful for some advice. I have a one-compartment model with first-order absorption, and get two subpopulations with different CL, the same Ka (factor almost equal to one between the Ka's of the two subpopulations, and A value of V that varies in one subpopulation but is almost the same for all subjects in the second subpopulation (very low ETA in that subpopulation). Questions: 1. Can I join the Ka's to have only one THETA(Ka) for both subpopulation? 2. How do I identify co-variates? Same procedure as without MIX, only separately for the two subpopulations? 3. The objective function went down by 55.14 from the model without covariates and without MIX, but the subpopulations do not appear meaningful. This applies also to the quite high (as compared to the estimate without MIX) volume of distribution that does not vary interindividually in one subpopulation. How do I deal with this result. Thank you in advance for your advice. Sincerely J. Ltsch _______________________________________________ Prof. Dr. med. Jrn Ltsch pharmazentrum frankfurt/ZAFES Institut fr Klinische Pharmakologie Johann Wolfgang Goethe-Universitt Theodor-Stern-Kai 7 D-60590 Frankfurt am Main Tel.:069-6301-4589 Fax.:069-6301-7636 http://www.klinik.uni-frankfurt.de/zpharm/klin/