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par2
2008 Sep 30
2
weird behavior of drop1() for polr models (MASS)
...tor terms. An example:
library("MASS");
options(contrasts = c("contr.treatment", "contr.poly"));
house.plr1 <- polr(Sat ~ Infl + Type + Cont, weights = Freq, data =
housing);
drop1(house.plr1,attributes(house.plr1$terms)$term.labels,test="Chisq");
house.plr2 <- polr(Sat ~ Infl * Type + Cont, weights = Freq, data =
housing);
drop1(house.plr2,attributes(house.plr2$terms)$term.labels,test="Chisq");
Notice that model 2 has a * instead of a + between predictors Infl and Type.
In model 1, estimated parameters are nicely attributed to the right...