From ripley at stats.ox.ac.uk  Mon Apr 14 09:32:10 2003
From: ripley at stats.ox.ac.uk (Prof Brian Ripley)
Date: Mon Apr 14 09:32:26 2003
Subject: [Rd] aliased coefficients in summary.glm
In-Reply-To: <5.1.0.14.2.20030410171330.01e816b8@mcmail.cis.mcmaster.ca>
Message-ID: <Pine.LNX.4.44.0304140829510.7075-100000@gannet.stats>

John,

This has only just arrived.  It is not a good time to be raising such 
issues (1.7.0 is frozen, so this would have to be for 1.8.0).  Could you 
send it as a wishlist item to R-bugs?  Otherwise it is very likely to be 
forgotten about.

Brian

On Thu, 10 Apr 2003, John Fox wrote:

> Dear list members,
> 
> I was reminded of what I see as a problem with summary.glm this week when 
> some of my students fell into a trap in a homework exercise, defining a 
> logit model in which coefficients were aliased. When this happens in lm, 
> summary.lm prints a message ["Coefficients: (1 not defined because of 
> singularities)"], but summary.glm is silent. In both instances, the print 
> methods show aliased coefficients as NA.
> 
> At minimum, I think that it would be desirable for summary.glm to indicate 
> that there's a problem. In addition, I would prefer that both summary.glm 
> and summary.lm include aliased coefficients (as NA) in the table of 
> coefficients.

-- 
Brian D. Ripley,                  ripley@stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595


[Rd] aliased coefficients in summary.glm
Prof Brian Ripley