[R] Ordinal Independent Variables

Rick Bilonick
Mon, 22 May 2006 22:23:05 -0000

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.