Plot differential test functioning

Draws the expected-score curves of the reference and one other group over the location scale, with the difference between them below.

Usage

plot_dtf(x, group = NULL, ...)

Arguments

x

A dtf result.

group

The group to draw; the first compared group by default.

...

Further arguments passed to plot for the expected-score panel, overriding its defaults.

Value

x, invisibly.

Examples

set.seed(2)
n <- 400
d <- seq(-1.5, 1.5, length.out = 8)
g <- rep(c("a", "b"), each = n / 2)
sh <- matrix(0, n, 8); sh[g == "b", 2:3] <- 0.8
X <- matrix(rbinom(n * 8, 1, plogis(outer(rnorm(n), d, "-") - sh)), n, 8)
colnames(X) <- paste0("I", 1:8)
fit <- rasch(data.frame(X, grp = g), factors = "grp")
plot_dtf(dtf(fit, by = "grp", items = c("I2", "I3")))