Plot category probability curves — plot_ccc • rasch

Plot category probability curves

Usage

plot_ccc(
  fit,
  item,
  grid = seq(-6, 6, 0.05),
  observed = FALSE,
  n_groups = fit$n_groups
)

Arguments

fit: A fitted object from rasch.
item: Item name or column index.
grid: Logit grid over which to draw the curves.
observed: Overlay the observed category proportions per class interval (Andrich and Marais 2019, ch. 20).
n_groups: Class intervals for the observed points.

Value

Called for its plotting side effect; invisibly NULL.

Examples

set.seed(1)
simP <- function(th, t) { x <- 0:length(t); p <- exp(x * th - c(0, cumsum(t))); p / sum(p) }
th <- rnorm(400)
X <- sapply(1:4, function(i) sapply(th, function(t) sample(0:3, 1, prob = simP(t, c(-1, 0, 1)))))
colnames(X) <- sprintf("P%02d", 1:4)
plot_ccc(rasch(X), "P01", observed = TRUE)