plot.Item | R Documentation |
Item
objectplot.Item
Plots the item characteristic curve for dichotomous items
and category response functions for polytomous items.
## S3 method for class 'Item' plot( x, theta_range = c(-4, 4), title = "", suppress_plot = FALSE, category_names = FALSE, legend_title = NULL, base_r_graph = FALSE, ... )
x |
An |
theta_range |
Either (a) a numeric vector of length two where the values are minimum and maximum theta values, or, (b) a numeric vector of length more than two where values represents the theta values that will be plotted. |
title |
Title of the plot. By default if the item is 1-4PM IRT model
then the title will be "Item Characteristic Curve" if the item
follows Graded Response Model the title will be
"Category Response Functions". Set it to |
suppress_plot |
If |
category_names |
If the model used is 'GRM' (Graded Response Model)
these names will serve as category names. For example,
c("Strongly Disagree", "Disagree", "Agree", "Strongly Agree").
The default is |
legend_title |
The title of the plot's legend. |
base_r_graph |
If |
... |
Additional arguments that will be passed to |
Depending on the value of suppress_plot
function either prints
the item characteristic curve or returns the plot object.
Emre Gonulates
plot(x = item(b = 0.3, D = 1, model = "1PL")) itm1 <- item(a = 1.2, b = 0.3, c = .2, model = "3PL") plot(itm1) plot(item(a = 1.2, b = 0.3, c = .2, d = .89, D = 1)) # Use base R graphics for the plot plot(itm1, base_r_graph = TRUE) # Plot Graded Response Model itm2 <- item(a = 0.902, b = c(-1.411, 0.385, 1.79), model = "GRM") plot(itm2) plot(itm2, category_names = c("Strongly Disagree", "Disagree", "Agree", "Strongly Agree")) plot(itm2, category_names = c("Strongly Disagree", "Disagree", "Agree", "Strongly Agree"), base_r_graph = TRUE) # A Graded Response Model item with two categories (i.e. 2PL item): itm3 <- item(a = 0.8, b = 1, model = "GRM") plot(itm3, category_names = c("Incorrect", "Correct"), legend_title = "Response") ## Not run: # Change the y-axis label (Only available if 'ggplot2' is installed) # plot(itm3, suppress_plot = TRUE) + ylab("New Label") ## End(Not run)
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