Plot an item characteristic curve — plot

Draws the model expected-score curve with observed class-interval means overlaid. With group supplied, observed means are drawn separately per group, the conventional graphical DIF display.

Usage

plot_icc(fit, item, group = NULL, n_groups = NULL, grid = seq(-5, 5, 0.05))

Arguments

fit: A fitted object from rasch.
item: Item name or column index.
group: Optional person grouping vector, or one or more names of factors nominated in the fit, for a DIF overlay; several names give the factor-combination cells (the factorial display).
n_groups: Number of class intervals for the observed means; by default the fit's own count, or – with a group overlay – a count adapted to keep the smallest group's interval cells adequately filled.
grid: Logit grid over which to draw the model curve.

Value

Called for its plotting side effect; invisibly NULL.

Examples

set.seed(1)
d <- seq(-2, 2, length.out = 6)
X <- matrix(rbinom(400 * 6, 1, plogis(outer(rnorm(400), d, "-"))), 400, 6)
colnames(X) <- sprintf("I%02d", 1:6)
plot_icc(rasch(X), "I03")