library(vcd) library(car) # for Anova() arth.polr <- polr(Improved ~ Sex + Treatment + Age, data=Arthritis) summary(arth.polr) Anova(arth.polr) # Type II tests library(effects) arth.effects <- allEffects(arth.polr, xlevels=list(age=seq(15,45,5)) ) plot(arth.effects) # visualize all main effects # plot terms not in model plot(effect("Sex:Age", arth.polr)) plot(effect("Treatment:Age", arth.polr))