Plot a Wright map

The conventional vertical person-item map (Wright and Stone 1979): the person distribution to the left of a shared logit axis and the item thresholds, labelled by item (and threshold number for polytomous items), stacked to its right.

Usage

plot_wright(fit, bins = 35, xlim = NULL, cex_labels = 0.8)

Arguments

fit

A fitted object from rasch.

bins

Number of bins for the person distribution and the threshold label rows.

xlim

Optional logit range for the shared scale; persons and thresholds outside it are omitted.

cex_labels

Character expansion for the threshold labels.

Value

Called for its plotting side effect; invisibly NULL.

References

Wright, B. D., & Stone, M. H. (1979). Best Test Design. Chicago: MESA Press.

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) <- paste0("I", 1:6)
plot_wright(rasch(X))