Plot a person characteristic curve — plot

The person characteristic curve: the probability of success as a function of item location at the person's estimated measure, with the person's observed responses overlaid, grouped into item-difficulty intervals (proportion of maximum score per interval). Erratic responding (for example lucky guessing on hard items by a low-proficiency person) shows as observed points far from the curve, complementing the person fit residual.

Usage

plot_pcc(fit, person, n_groups = 5, grid = seq(-5, 5, 0.05))

Arguments

fit: A fitted object from rasch.
person: Row number of the person, or an ID matching fit$person$id.
n_groups: Number of item-difficulty intervals for the observed points (capped by the number of observed items).
grid: Item-location grid over which to draw the curve.

Value

Called for its plotting side effect; invisibly NULL.

Examples

set.seed(1)
d <- seq(-2, 2, length.out = 12)
X <- matrix(rbinom(300 * 12, 1, plogis(outer(rnorm(300), d, "-"))), 300, 12)
colnames(X) <- paste0("I", 1:12)
plot_pcc(rasch(X), person = 1)