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

[Pang Du]

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]]
> 
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-- 
Andrew Robinson  
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