Hello all,

 

I have an ordered factor that I would like to include in the linear
predictor of a binomial glm, where the estimated coefficients are
constrained to be monotonic. Does anyone know how to do this? I've tried
using an ordered factor but this does not have the desired effect, an
(artificial) example of this follows;

 

n <- 100

strings <- sample(c("low", "med", "high"), n, TRUE)

 

x.ordered <- ordered(strings, c("low", "med", "high"))

x.unordered <- factor(strings)

 

pr <- ifelse(strings == "low", 0.4, ifelse(strings == "med", 0.3, 0.2))

 

y <- rbinom(n, 1, pr)

 

mod.ordered <- glm(y ~ x.ordered, binomial)

mod.unordered <- glm(y ~ x.unordered, binomial)

 

summary(mod.ordered)

summary(mod.unordered)

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