Re: nonmem question regarding condition number
Dear Laureen,
High condition number represents overparametrization. You must check also the
correlation matrix for potential correlations above 0.95 between parameters. If
you strongly feel on the biological basis that your drug is a 3 compartment
model, then you may fix some of the parameters of 3 compartment model such as
Q1,Q2 based on prior data and estimate other parameters to see if your
diagnostics make sense. Parameters with high SEs could be your clues to the
problems. In my opinion, you have informative data with 12 samples per
subjects(hopefully at the informative time points) to have a complex model.
Best Regards,
Ayyappa
Quoted reply history
> On Mar 24, 2016, at 5:10 AM, L.A. ten Berg - Lammers
> <[email protected]> wrote:
>
> Dear nmusers,
> I am currently analyzing PK profiles after a single iv adminstration.
> Volunteers were sampled frequently: 12 samples per curve.
> For the structural model 2- and a 3-compartment models are compared. The
> CWRES vs time plot of the 2-compartment shows the typical wave, indicative
> for a 3-compartment model. Introduction of a third compartment eliminated the
> wave, OFV decreased with 180 points, precision of the estimates did change
> notably, but the condition number increased from 998 to 2.0*E16.
> Does anyone know how to interpret this large increase in condition number?
> Best wishes,
> Laureen ten Berg
>
>
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>
>
> Laureen ten Berg-Lammers
> Hospital Pharmacist
>
> Academisch Medisch Centrum
> Universiteit van Amsterdam
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