Plot Item and Test Information Functions

This method plots item or test information functions for a specified set of theta values. It can also display the conditional standard error of estimation (CSEE) at the test level.

Usage

# S3 method for class 'info'
plot(
  x,
  item.loc = NULL,
  overlap = FALSE,
  csee = FALSE,
  xlab.text,
  ylab.text,
  main.text,
  lab.size = 15,
  main.size = 15,
  axis.size = 15,
  line.color,
  line.size = 1,
  layout.col = 4,
  strip.size = 12,
  ...
)

Arguments

x: x An object of class info obtained from info().
item.loc: A numeric vector indicating which item information functions to plot, specified by item position (e.g., 1 for the first item). If NULL (default), the test information function for the entire test form is plotted.
overlap: Logical. If TRUE, multiple item information functions are plotted in a single panel. If FALSE (default), each item information function is displayed in a separate panel.
csee: Logical. If TRUE, plots the conditional standard error of estimation (CSEE) at the test level. Note that the CSEE plot is only available at the test level, not for individual items. If FALSE (default), item or test information functions are plotted.
xlab.text, ylab.text: Character strings specifying the labels for the x and y axes, respectively.
main.text: Character string specifying the overall title of the plot.
lab.size: Numeric value specifying the font size of axis titles. Default is 15.
main.size: Numeric value specifying the font size of the plot title. Default is 15.
axis.size: Numeric value specifying the font size of axis tick labels. Default is 15.
line.color: A character string specifying the color of the plot lines. See http://www.cookbook-r.com/Graphs/Colors_(ggplot2)/ for available color names.
line.size: Numeric value specifying the thickness of plot lines. Default is 1.
layout.col: Integer. Number of columns to use when faceting multiple item information functions. Used only when overlap = FALSE. Default is 4.
strip.size: Numeric value specifying the font size of facet labels when multiple items are displayed.
...: Additional arguments passed to ggplot2::geom_line() from the ggplot2 package.

Value

This method function displays the item or test information function plot. When csee = TRUE, the CSEE is returned at the test level.

Details

All of the plots are drawn using the ggplot2 package. The object of class info can be obtained from the function info().

Author

Hwanggyu Lim hglim83@gmail.com

Examples


if (FALSE) { # \dontrun{
## Example using a "-prm.txt" file exported from flexMIRT

# Import the "-prm.txt" output file from flexMIRT
flex_prm <- system.file("extdata", "flexmirt_sample-prm.txt", package = "irtQ")

# Read the item parameters and convert them to item metadata
test_flex <- bring.flexmirt(file = flex_prm, "par")$Group1$full_df

# Define a sequence of theta values
theta <- seq(-4, 4, 0.1)

# Compute item and test information values for the given theta values
x <- info(x = test_flex, theta = theta, D = 1, tif = TRUE)

# Plot the test information function
plot(x)

# Plot the item information function for the second item
plot(x, item.loc = 2)

# Plot multiple item information functions, each in a separate panel
plot(x, item.loc = 1:8, overlap = FALSE)

# Plot multiple item information functions in a single panel
plot(x, item.loc = 1:8, overlap = TRUE)

# Plot the conditional standard error of estimation (CSEE) at the test level
plot(x, csee = TRUE)

} # }