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. Thanks for your attention, John ----------------------------------------------------- John Fox Department of Sociology McMaster University Hamilton, Ontario, Canada L8S 4M4 email: jfox@mcmaster.ca phone: 905-525-9140x23604 web: www.socsci.mcmaster.ca/jfox -----------------------------------------------------
aliased coefficients in summary.glm
2 messages · John Fox, Brian Ripley
3 days later
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