plot.Itempool: Plot Item Characteristic Curves or Test Characteristic Curve...

View source: R/plot_itempool.R

plot.ItempoolR Documentation

Plot Item Characteristic Curves or Test Characteristic Curve of an Itempool object


plot.Itempool plots the item characteristic curves (item response curves) or test characteristic curve of an Itempool-class object.


## S3 method for class 'Itempool'
  theta_range = c(-4, 4),
  type = "icc",
  tcc_prop_corr = FALSE,
  focus_item = NULL,
  title = "",
  suppress_plot = FALSE,
  legend_title = NULL,
  base_r_graph = FALSE,
  y_lim = NULL,



An Itempool-class object.


Either a numeric vector of length two setting the boundaries of x-axis, e.g. c(-4, 4), or, a numeric vector that is includes the theta values that will be plotted, e.g. seq(-3, 3, by = 0.1).


The type of the graph. The default value is "icc". Available options are:


Plot item characteristic curve of each item


Plot test characteristic curve


Plot histograms of item parameters


Plot dot plot of item parameters


If TRUE, test characteristic curve will be show the proportion correct of the test (i.e. the range of y-axis will be 0-1 instead of 0 to the number of items).


A character string of the 'item_id' of the item to be focused. If type = "pars", this item will be shown with a red dot to distinguish it from others.


Title of the plot. Set title = NULL to suppress the plot title. The default is "". If type = "tcc" and title = "", title will be 'Test Characteristic Curve'. If type = "icc" and title = "", title will be 'Item Characteristic Curve'. If type = "hist" or type = "pars" and title = "", title will be 'Parameter Values'.


If FALSE the function will print the plot. If TRUE, function will return the plot object. Default value is FALSE.


The title of the plot's legend.


If TRUE function will plot graphs using base R graphics. If FALSE the function will check whether 'ggplot2' package is installed. If it is installed, it will use 'ggplot2' package for the plot. The default value is FALSE.


A numeric vector of length two representing the lower and upper bound of y-axis.


Additional arguments that will be passed to geom_line


Depending on the value of suppress_plot function either prints the item characteristic curve or returns the plot object.


Emre Gonulates


ip <- generate_ip(n = sample(10:15,1))

# Additional arguments will passed to geom_line
plot(ip, size = .25, alpha = 0.3)

# Set the boundaries of the graph
plot(ip, theta_range = c(-2, 2))
# alternatively provide theta values
plot(ip, theta_range = seq(-6, 6, by = 0.25))

# Test Characteristic Curve
plot(ip, type = "tcc")

# Proportion correct for test characteristic curve
plot(ip, type = "tcc", tcc_prop_corr = TRUE)

# Plot histogram of item parameters
plot(ip, type = "hist")

## Not run: 
# Item parameter summary
ip <- generate_ip(n = 200)
plot(ip, type = "pars")
plot(ip, type = "pars", dotsize = .75)
plot(ip, type = "pars", focus_item = "Item_22")
# Use base R graphics
plot(ip, type = "pars", base_r_graph = TRUE)

# # Remove the legend altogether
# plot(ip, suppress_plot = TRUE) + ggplot2::theme(legend.position="none")
# # Change the labels:
# plot(ip, suppress_plot = TRUE) +
#   ylab("Probability") + xlab("Ability Score")

## End(Not run)

irt documentation built on Nov. 10, 2022, 5:50 p.m.