This is about the covariates, not the dependent variable. So a polynomial logistic regression seems hardly appropriate.
David is right with his latest statement, just because they are ordered does not assure that the effect is monotonic. If the "low", "medium", and "high" groups had even spacing (e.g., 10, 20, 30 (on whatever scale)), you could use an alternative way of factor coding. Orthogonal polynomial contrasts tests for curvilinear effects by while keeping the factor nature of the variable intact. That is, it is not the same as including the numeric variable and its higher order polynomials (e.g., Rosenthal and Rosnow 1985). Daniel ------------------------- cuncta stricte discussurus ------------------------- -----Original Message----- From: r-help-boun...@r-project.org [mailto:r-help-boun...@r-project.org] On Behalf Of C.H. Sent: Sunday, March 28, 2010 11:10 PM To: Ravi Kulkarni Cc: r-help@r-project.org Subject: Re: [R] Coding of categorical variables for logistic regression? ?polr of the MASS package. On Mon, Mar 29, 2010 at 10:39 AM, Ravi Kulkarni <ravi.k...@gmail.com> wrote: > > How do I use the "extra" information that two of my predictors are ordinal? > (I did not know I could do that.) > > Thanks, > Ravi > -- > View this message in context: > http://n4.nabble.com/Coding-of-categorical-variables-for-logistic-regression-tp1694250p1694644.html > Sent from the R help mailing list archive at Nabble.com. > > ______________________________________________ > R-help@r-project.org mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide http://www.R-project.org/posting-guide.html > and provide commented, minimal, self-contained, reproducible code. > -- CH Chan Research Assistant - KWH http://www.macgrass.com ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code. ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
