Re: Change of NSIG or R matrix
Xinting,
I ignore rounding errors and failure of the covariance step when model building. Indeed you will speed up your model building by not using $COV. I build my models based on 1) change in OFV 2) plausibility of parameter estimates 3) VPCs.
i would not trust parameter estimates obtained with NSIG<3.
I use non-parametric bootstraps to also help in model building but would never rely on confidence intervals derived from $COV SEs.
Nick
Quoted reply history
On 8/10/2013 8:57 p.m., Xinting Wang wrote:
> Dear all,
>
> I have a naive question regarding the modeling building process in NONMEM. With more and more covariates added in the model, I often come across an error message saying that "ERROR 134", or R MATRIX SINGULAR.
>
> After searching from the internet, I learned that changing NSIG in $ESTIMATION and MATRIX=S in $COV would be helpful for both problems respectively. And from my own experience, it dose help with the modeling building.
>
> However, my concern is, I used different NSIG and MATRIX in the previous steps. Is it proper to use different NSIGs and MATRICE in a single model building? If not, could you please explain this a little bit?
>
> Thank you in advance!
>
> Best Regards
> --
> Xinting
> Wang
--
Nick Holford, Professor Clinical Pharmacology
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