Michael Friendly wrote:
For the following model,
library(vcd)
arth.polr <- polr(Improved ~ Sex + Treatment + Age, data=Arthritis)
summary(arth.polr)
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.
That test is anti-conservative. I like graphical methods using partial
residual plots as in my book. See the following reference. -Frank
@ARTICLE{pet90par,
author = {Peterson, Bercedis and Harrell, Frank E.},
year = 1990,
title = {Partial proportional odds models for ordinal response
variables},
journal = Applied Statistics,
volume = 39,
pages = {205-217}
}
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?
--
Frank E Harrell Jr Professor and Chair School of Medicine
Department of Biostatistics Vanderbilt University
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