Re: OMEGA BLOCK with mixture model?

Hi, It is indeed a nuisance to have to renumber all the ETAs if you have a complex model and you change the sequence of $OMEGA. You can of course choose to use the awk script which comes with WFN ( http://wfn.sourceforge.net ) translate an extended NM-TRAN control stream, which uses parameter names for THETA, ETA and EPS (or ERR) references in the abbreviated code, into a standard NM-TRAN format with all the renumbering taken care of automatically. This awk script can be used with any installation of NONMEM that runs an operating system that has a version of awk available. It is not necessary to use WFN. Typically a one or two line change is needed in your favourite script for running NONMEM to allow the translation to take place. Nick [email protected] wrote: > Nele, > > going by the nonmem user manual, part VIII, p 94 ($OMEGA), "If FIXED appears anywhere among the list of values, the entire block is fixed." > > I did not see anyone pointing that out yet. > > This does in fact imply that you need to reorder the sequence of random effects (which can be quite a nuisance if you have a sequence of models and the parameters do not correspond any more across models). > > Andreas > > ----- > > Andreas Krause, PhD > Lead Scientist Modeling and Simulation > > Actelion Pharmaceuticals Ltd / Gewerbestrasse 16 / CH-4123 Allschwil / Switzerland > > phone +41 61 565 6891 / fax +41 61 565 66 96 > [email protected] / www.actelion.com > > *[email protected]* > Sent by: [email protected] > > 04/14/2009 05:08 PM > > To > [email protected] > cc > > Subject > [NMusers] OMEGA BLOCK with mixture model? > > 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. 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