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Re: [S] parentheses in interaction terms

To: Isabelle Robichaud <eir8049@umoncton.ca>
Subject: Re: [S] parentheses in interaction terms
From: "Charles E. (Ted) Wright" <cew@aris.ss.uci.edu>
Date: Fri, 22 Jan 1999 06:46:41 -0800 (PST)
Cc: s-news@wubios.wustl.edu
In-reply-to: <199901221059.SAA18939@cyllene.uwa.edu.au>
Sender: owner-s-news@wubios.wustl.edu
Please summarize the responses you receive to this question for the rest of
us.

Thanks,

Ted Wright

On Fri, 22 Jan 1999, Isabelle Robichaud wrote:

> 
> Dear fellow S-Plus users,
> 
> I am relatively new at S-Plus, which might explain my question, but 
> I have come across a behavior that puzzles me.  Any 
> insight/comments would be very appreciated.
> 
> I obtain different results whether I put parentheses or not around 
> the terms in interactions.  For example, glm(RESP ~ X1:X2) gives 
> different results from glm(RESP ~ (X1):(X2)).  In fact, the second 
> model gives the same deviance and df as glm(RESP ~ X1*X2) 
> does.  Is this normal?  (X1 is a continuous variable, X2 is an 
> ordered factor.)
> 
> Sorry if the question is evident to everyone but me.  Thanks in 
> advance!
> 
> Isabelle
> p.s. I work with version 4.5 (professional, release 2) on a Pentium 
> 233, 32 M of RAM.
> 
> Isabelle Robichaud
> Departement de biologie
> Universite de Moncton
> Moncton NB Canada E1A 3E9
> e-mail: eir8049@umoncton.ca
> 
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