Plot the residual-correlation heatmap

Only the lower triangle is drawn – the matrix is symmetric, so each pair is shown once. With stat = "q3star" (the default) cells are coloured by Q3* – each pair's residual correlation minus the average off-diagonal correlation – so white marks the value expected under local independence and warm colour marks dependence; with stat = "q3" the raw residual correlation is coloured, white at zero. The scale saturates at cap rather than the +/-1 of an ordinary correlation: a residual correlation seldom reaches even 0.5 under a fitting model (the conventional flag is Q3* above 0.2; Christensen, Makransky and Horton 2017), so the colour is spent where the values actually discriminate.

Usage

plot_resid_cor(fit, stat = c("q3star", "q3"), cap = 0.5)

Arguments

fit

A fitted object from rasch.

stat

Which statistic to colour: "q3star" (adjusted Q3, the default) or "q3" (the raw residual correlation).

cap

Value at which the colour saturates (default 0.5).

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