Plot All Item Characteristic Curves Overlaid from exametrika

This function takes exametrika IRT output as input and generates an overlay plot of all Item Characteristic Curves (ICC) using ggplot2. All item curves are displayed on a single graph for easy comparison.

Usage

plotICC_overlay_gg(
  data,
  items = NULL,
  xvariable = c(-4, 4),
  title = TRUE,
  colors = NULL,
  linetype = "solid",
  show_legend = TRUE,
  legend_position = "right"
)

Arguments

data: An object of class c("exametrika", "IRT") from exametrika::IRT().
items: Numeric vector specifying which items to plot. If NULL (default), all items are plotted.
xvariable: A numeric vector of length 2 specifying the range of the x-axis (ability). Default is c(-4, 4).
title: Logical or character. If TRUE (default), display an auto-generated title. If FALSE, no title. If a character string, use it as a custom title.
colors: Character vector of colors for each item. If NULL (default), a colorblind-friendly palette is used.
linetype: Character or numeric specifying the line type. Can be a single value for all items or a vector for each item. Default is "solid".
show_legend: Logical. If TRUE (default), display the legend.
legend_position: Character. Position of the legend. One of "right" (default), "top", "bottom", "left", "none".

Value

A single ggplot object showing all Item Characteristic Curves overlaid on one graph.

Details

This function is similar to calling plot(IRT_result, type = "IRF", overlay = TRUE) in the exametrika package, but returns a ggplot2 object that can be further customized.

The ICC is computed using the four-parameter logistic model: $$P(\theta) = c + \frac{d - c}{1 + \exp(-a(\theta - b))}$$

Examples

library(exametrika)
result <- IRT(J15S500, model = 3)
plotICC_overlay_gg(result) # All items

plotICC_overlay_gg(result, items = 1:5) # First 5 items only

plotICC_overlay_gg(result, title = "My Custom Title", show_legend = TRUE)