Question

Probably pretty easy, but I want to know, how to grab coefficients when using the zeroinfl command?

treatment <- factor(rep(c(1, 2), c(43, 41)), 
    levels = c(1, 2),labels = c("placebo", "treated"))
improved <- factor(rep(c(1, 2, 3, 1, 2, 3), c(29, 7, 7, 13, 7, 21)),
    levels = c(1, 2, 3),labels = c("none", "some", "marked"))

numberofdrugs <- rpois(84, 2)
healthvalue <- rpois(84,0.5)
y <- data.frame(healthvalue,numberofdrugs, treatment, improved)

require(pscl)
ZIP<-zeroinfl(healthvalue~numberofdrugs+treatment+improved, y)

summary(ZIP)

I usually use ZIP$coef[1] to grab a coefficient, but unfortunately here you grab a whole bunch. So how can I grab one single coeficients from a ZIP model?

Answer 1

Use the coef extraction function to list all coefficients in one long vector, and then you can use single index notation to select them:

coef(ZIP)[1]

count_(Intercept) 
        0.1128742 

Alternatively, you need to select which model you want to get the coefficients from first:

ZIP$coef$count[1]

(Intercept) 
  0.1128742

ZIP$coef[[1]][1]

(Intercept) 
  0.1128742