Re: OMEGA BLOCK with mixture model?

This should do the trick (rename ETAs): $OMEGA BLOCK(3) 0.1 ;CL1 0.01 0.1 ;F1 0 0.01 0.1 ;CL2 (do not FIX anything) Although I am not sure whether you need to estimate F1 for oral data (without IV). You could try to use ETA on V instead of ETA on F1. Leonid -------------------------------------- Leonid Gibiansky, Ph.D. President, QuantPharm LLC web: www.quantpharm.com e-mail: LGibiansky at quantpharm.com tel: (301) 767 5566 [email protected] wrote: > Dear all, > > I am trying to fit a PK model to oral data. In the data, we observed two things: First, CL seems to be negatively correlated with F1. Secondly, there seem to be two subpopulations in the exposure, let's say a large group with 'normal' and a second group with high exposure. I would like to identify the subpopulations using a mixture model, but keep the correlation between CL and F1. Now I ran into problems when coding the $OMEGA BLOCK. > > I figured the block to be something like: > $OMEGA BLOCK(3) > 0.1 ;CL1 > 0 FIX 0.1 ;CL2 > 0.01 0.01 0.1 ;F1 > > The error message that appears is: > a covariance is zero, but the block is not a band matrix > > I assume that this means that I am not allowed to fix the correlation between the two clearance-omegas to zero. However, it would be unreasonable to allow a correlation, because the omegas belong to different subpopulations, so there can't be a correlation. On the other hand, I did not include subpopulations for F1, so how can I keep this correlation to both CL-subgroups? > > Any thoughts on this would be highly appreciated! > Best wishes > Nele > ______________________________________________________________ > > Dr. Nele Plock > Pharmacometrics -- Modeling and Simulation > > Nycomed GmbH > Byk-Gulden-Str. 2 > D-78467 Konstanz, Germany > > Fon: (+49) 7531 / 84 - 4759 > Fax: (+49) 7531 / 84 - 94759 > > mailto: [email protected] > http://www.nycomed.com > > County Court: Freiburg, Commercial Register HRB 701257 > Chairman Supervisory Board: Charles Depasse > > Management Board: Dr. Barthold Piening, Gilbert Rademacher, Dr. Anders Ullman > > ---------------------------------------------------------------------- > Proprietary or confidential information belonging to Nycomed Group may > be contained in this message. If you are not the addressee indicated > in this message, please do not copy or deliver this message to anyone. > In such case, please destroy this message and notify the sender by > reply e-mail. Please advise the sender immediately if you or your > employer do not consent to Internet e-mail for messages of this kind. > Opinions, conclusions and other information in this message that > pertain to the sender's employer and its products and services > represent the opinion of the sender and do not necessarily represent > or reflect the views and opinions of the employer. >