Plot multiple-choice option curves — plot

The proportion choosing each response option across class intervals of the rest measure (the person estimate from the other items), with the keyed option drawn solid and bold. The curves are descriptive. Under ordered option scoring, higher-scored options should tend to occur at higher rest measures; an intermediate-credit option may peak in the middle.

Usage

plot_distractors(fit, item, n_groups = NULL)

Arguments

fit: A fitted object from rasch run with a key.
item: Keyed item name.
n_groups: Number of class intervals. By default, use the fit's count, with at least two requested intervals. Tied locations may produce fewer intervals.

Value

Called for its plotting side effect; invisibly NULL.

Examples

set.seed(1); Np <- 400
th <- rnorm(Np)
raw <- sapply(seq(-1, 1, length.out = 6), function(d) {
  ok <- rbinom(Np, 1, plogis(th - d))
  ifelse(ok == 1, "A", sample(c("B", "C", "D"), Np, replace = TRUE))
})
colnames(raw) <- paste0("M", 1:6)
fit <- rasch(raw, key = setNames(rep("A", 6), colnames(raw)))
plot_distractors(fit, "M3")