WrightMap Tutorial - Part 2

Plotting Items in Different Ways

Author

David Torres Irribarra & Rebecca Freund

Published

September 25, 2024

Plotting the Items in Different Ways

Updated September 2024 for changes in version 1.4.

Setup

We start by creating mock person and item estimates.

For the person proficiencies, we create a matrix with 1000 values per dimension (5 dimensions in total).

set.seed(2020)
mdim.sim.thetas <- matrix(rnorm(5000), ncol = 5)

Dealing with Many, Many Items

What happens if you have too many items?

rasch2.sim.thresholds <- runif(50, -3, 3)

If we use the defaults…

wrightMap(rnorm(1000), rasch2.sim.thresholds)

Things do not look quite right.

WrightMap offers some options…

rasch.sim.thetas <- rnorm(1000)
rasch2.sim.thresholds <- runif(10, -3, 3)

You can use the itemClassic or itemHist options for item.side.

wrightMap(rasch.sim.thetas, rasch2.sim.thresholds, item.side = itemClassic, item.prop = .5)

wrightMap(rasch.sim.thetas, rasch2.sim.thresholds, item.side = itemHist, item.prop = 0.5)

Or you can play with the way labels are presented:

wrightMap(rnorm(1000), rasch2.sim.thresholds, show.thr.lab = FALSE, label.items.srt = 45)

wrightMap(rnorm(1000), rasch2.sim.thresholds, show.thr.lab = FALSE, label.items.rows = 2)

wrightMap(rnorm(1000), rasch2.sim.thresholds, show.thr.lab = FALSE, label.items = c(1:50), label.items.rows = 3)

Or you can get rid of that axis completely.

wrightMap(rnorm(1000), rasch2.sim.thresholds, show.thr.sym = FALSE,
    thr.lab.text = paste("I", 1:10, sep = ""), label.items = "", label.items.ticks = FALSE)