From: Andrew Robinson <A.Robinson_at_ms.unimelb.edu.au>

Date: Fri, 06 May 2011 09:55:17 +1000

Date: Fri, 06 May 2011 09:55:17 +1000

Even then, I think that there's a problem. If C is in the model, then the response varies by C. The simplest way is to pick a value for C, and then evaluate the group mean estimates of A and B (and C).

Something in my brain keeps asking whether another way to marginalize C for the purposes of predicting A and B is just to remove it from the model, or alternatively to make it a random effect. Neither idea seems rock solid at this point.

Cheers

Andrew

On Thu, May 05, 2011 at 09:37:15AM -0400, Pang Du wrote:

> Oops, I hope not too. Don't know why I had the brackets around B+C. My

*> model is actually A*B+C. And I'm not sure how to obtain the two-way
**> prediction of AB with C marginalized. Thanks.
**>
**> Pang
**>
**> -----Original Message-----
**> From: Andrew Robinson [mailto:A.Robinson_at_ms.unimelb.edu.au]
**> Sent: Wednesday, May 04, 2011 10:13 PM
**> To: Pang Du
**> Cc: r-help_at_r-project.org
**> Subject: Re: [R] two-way group mean prediction in survreg with three factors
**>
**> I hope not!
**>
**> Facetiousness aside, the model that you have fit contains C, and,
**> indeed, an interaction between A and C. So, the effect of A upon the
**> response variable depends on the level of C. The summary you want
**> must marginalize C somehow, probably by a weighted or unweighted
**> average across its levels. What does that summary really mean? Can
**> you meaningfully average across the levels of a predictor that is
**> included in the model as a main and an interaction term?
**>
**> Best wishes
**>
**> Andrew
**>
**> On Wed, May 04, 2011 at 12:24:50PM -0400, Pang Du wrote:
**> > I'm fitting a regression model for censored data with three categorical
**> > predictors, say A, B, C. My final model based on the survreg function is
**> >
**> > Surv(..) ~ A*(B+C).
**> >
**> > I know the three-way group mean estimates can be computed using the
**> predict
**> > function. But is there any way to obtain two-way group mean estimates, say
**> > estimated group mean for (A1, B1)-group? The sample group means don't
**> > incorporate censoring and thus may not be appropriate here.
**> >
**> >
**> >
**> > Pang Du
**> >
**> > Virginia Tech
**> >
**> >
**> > [[alternative HTML version deleted]]
**> >
**> > ______________________________________________
**> > R-help_at_r-project.org mailing list
**> > https://stat.ethz.ch/mailman/listinfo/r-help
**> > PLEASE do read the posting guide
**> http://www.R-project.org/posting-guide.html
**> > and provide commented, minimal, self-contained, reproducible code.
**>
**> --
**> Andrew Robinson
**> Program Manager, ACERA
**> Department of Mathematics and Statistics Tel: +61-3-8344-6410
**> University of Melbourne, VIC 3010 Australia (prefer email)
**> http://www.ms.unimelb.edu.au/~andrewpr Fax: +61-3-8344-4599
**> http://www.acera.unimelb.edu.au/
**>
**> Forest Analytics with R (Springer, 2011)
**> http://www.ms.unimelb.edu.au/FAwR/
**> Introduction to Scientific Programming and Simulation using R (CRC, 2009):
**> http://www.ms.unimelb.edu.au/spuRs/
*

-- Andrew Robinson Program Manager, ACERA Department of Mathematics and Statistics Tel: +61-3-8344-6410 University of Melbourne, VIC 3010 Australia (prefer email) http://www.ms.unimelb.edu.au/~andrewpr Fax: +61-3-8344-4599 http://www.acera.unimelb.edu.au/ Forest Analytics with R (Springer, 2011) http://www.ms.unimelb.edu.au/FAwR/ Introduction to Scientific Programming and Simulation using R (CRC, 2009): http://www.ms.unimelb.edu.au/spuRs/ ______________________________________________ R-help_at_r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.Received on Thu 05 May 2011 - 23:57:52 GMT

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