Re: [R] two-way group mean prediction in survreg with three factors

From: Andrew Robinson <A.Robinson_at_ms.unimelb.edu.au>
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
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> > PLEASE do read the posting guide
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>
> --
> 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/

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Received on Thu 05 May 2011 - 23:57:52 GMT

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