[Rd] aliased coefficients in summary.glm

John Fox jfox at mcmaster.ca
Thu Apr 10 18:23:37 MEST 2003

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 

Thanks for your attention,
John Fox
Department of Sociology
McMaster University
Hamilton, Ontario, Canada L8S 4M4
email: jfox at mcmaster.ca
phone: 905-525-9140x23604
web: www.socsci.mcmaster.ca/jfox

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