NONMEM Users Network Archive

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RE: [External] Re: RE: Stepwise covariate modeling

From: Singla, Sumeet K <sumeet-singla>
Date: Tue, 29 Oct 2019 15:47:46 +0000

Thank you everyone for taking time out of your busy schedule to reply to my=
 question. I think all points were excellent. Gives me more to think about =
how to proceed from here and make more informed decision about my model.


-----Original Message-----
From: Leonid Gibiansky <lgibiansky
Sent: Tuesday, October 29, 2019 10:36 AM
To: Luann Phillips <Luann.Phillips
Subject: [External] Re: [NMusers] RE: Stepwise covariate modeling

I think we are making it more difficult than needed, especially for the peo=
ple who just started using the NLME. It does not hurt to include statistica=
lly significant covariate in the model even if the actual effect is small a=
nd does no manifest itself on the standard diagnostic plots.

It make sense to check whether there is an error in the model code.
Plots of random effects versus covariates of interest should help to see wh=
ether covariate model changed the individual random effects. If not (that i=
s, random effects of the model with and without covariate effect are numeri=
cally identical) then the coding is wrong and should be checked.


On 10/29/2019 11:00 AM, Luann Phillips wrote:
> Hi,
> If _all_ of the individual predictions are the same for the model with
> the covariate and without the covariate, then it sounds like the
> original model is at a local minimum instead of a global minimum.
> Best regards,
> Luann
> *From:* owner-nmusers
> *On Behalf Of *Singla, Sumeet K
> *Sent:* Tuesday, October 29, 2019 10:00 AM
> *To:* nmusers
> *Subject:* [NMusers] Stepwise covariate modeling
> Hi!
> I am performing stepwise covariate modeling using PsN feature in Pirana.=
> I am getting some covariates which are statistically reducing OFV
> significantly, however, when I include those covariates in the PK
> model, the results I am getting are exactly similar to what I am
> getting in my base model, i.e. there is no difference in individual
> predictions or pop predictions or any other diagnostic plots. So, does
> that mean I should move forward WITHOUT including those covariates as
> they don't seem to be explaining inter-individual variability despite
> scm telling me that they are statistically significant?
> Regards,
> *Sumeet K. Singla*
> *Ph.D. Candidate*
> *Division of Pharmaceutics and Translational Therapeutics*
> *College of Pharmacy | University of Iowa*
> *Iowa City, Iowa*
> *sumeet-singla
> *518.577.5881*
Received on Tue Oct 29 2019 - 11:47:46 EDT

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