[R] polr (MASS): score test for proportional odds model

Michael Friendly friendly at yorku.ca
Wed Feb 25 00:30:51 CET 2009

For the following model,

arth.polr <- polr(Improved ~ Sex + Treatment + Age, data=Arthritis)

where Improved is an ordered, 3-level response I'm looking for a 
*simple* way to test
the validity of the proportional odds assumption, typically done via a 
score test
for equal slopes/effects over the predictors.

I do find a po.test= option in the repolr package for repeated measures, 
but for my
(tutorial) purposes this is too complex.  Did I miss something simpler?

Michael Friendly     Email: friendly AT yorku DOT ca 
Professor, Psychology Dept.
York University      Voice: 416 736-5115 x66249 Fax: 416 736-5814
4700 Keele Street    http://www.math.yorku.ca/SCS/friendly.html
Toronto, ONT  M3J 1P3 CANADA

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