Rick Bilonick wrote: > When I run "lrm" from the Design package, I get a warning about > contrasts when I include an ordinal variable: > > Warning message: > Variable ordfac is an ordered factor. > You should set > options(contrasts=c("contr.treatment","contr.treatment")) > or Design will not work properly. in: Design(eval(m, sys.parent())) > > I don't get this message if I use glm with family=binomial. It produces > linear and quadratic contrasts. > > If it's improper to do this for an ordinal variable, why does glm not > balk? > > Rick B.
Standard regression methods don't make good use of ordinal predictors and just have to treat them as categorical. Design is a bit picky about this. If the predictor has numeric scores for the categories, you can get a test of adequacy of the scores (with k-2 d.f. for k categories) by using scored(predictor) in the formula. Or just create a factor( ) variable to hand to Design. -- Frank E Harrell Jr Professor and Chair School of Medicine Department of Biostatistics Vanderbilt University ______________________________________________ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html