Information Plots for IRT Models
Base graphics plotting function for information plot visualization of IRT models.
infoplot(object, what = c("categories", "items", "test"),
ref = NULL, items = NULL, names = NULL, layout = NULL, xlim = NULL,
ylim = NULL, col = NULL, lty = NULL, lwd = NULL, main = NULL, legend = TRUE,
xlab = "Latent trait", ylab = "Information", add = FALSE, ...)object |
a fitted model object of class |
what |
character, specifying the type of information to visualize. |
ref |
argument passed over to internal calls of |
items |
character or numeric, specifying the items for which information curves should be visualized. |
names |
character, specifying labels for the items. |
layout |
matrix, specifying how the item or category information curves
of different items should be arranged. If |
xlim, ylim |
numeric, specifying the x and y axis limits. |
col |
character, specifying the colors of the test, item or category information curves. |
lty |
numeric, specifying the line type of the information curves. |
lwd |
numeric, specifying the line width of the information curves. |
main |
character, specifying the overall title of the plot. |
legend |
logical, specifying if a legend is drawn when multiple item
information curves are overlayed. The labels in the legend correspond to
the item names (which can be specified in the argument |
xlab, ylab |
character, specifying the x and y axis labels. |
add |
logical. If |
... |
further arguments passed to internal calls of
|
The information plot visualization illustrates the test, item or category
information as a function of the ability parameter θ under a
certain IRT model. Further details on the computation of the displayed
information can be found on the help page of the function
predict.pcmodel.
## load verbal aggression data
data("VerbalAggression", package = "psychotools")
## fit Rasch and partial credit model to verbal aggression data
rmmod <- raschmodel(VerbalAggression$resp2)
pcmod <- pcmodel(VerbalAggression$resp)
## category information plots for all items under the dichotomous RM
plot(rmmod, type = "information", what = "categories")
## category information plots for all items under the PCM
plot(pcmod, type = "information", what = "categories")
## overlayed item information plots for the first six items of the
## data set under the PCM
plot(pcmod, type = "information", what = "items", items = 1:6)
## a comparison of the item information for the first six items under the
## dichotomous RM and the PCM
plot(pcmod, type = "information", what = "items", items = 1:6,
xlim = c(-5, 5))
plot(rmmod, type = "information", what = "items", items = 1:6,
lty = 2, add = TRUE)
legend(x = "topright", legend = c("PCM", "RM"), lty = 1:2, bty = "n")
## a comparison of the test information based on all items of the
## data set under the dichotomous RM and the PCM
plot(pcmod, type = "information", what = "test", items = 1:6, xlim = c(-5, 5))
plot(rmmod, type = "information", what = "test", items = 1:6, lty = 2,
add = TRUE)
legend(x = "topright", legend = c("PCM", "RM"), lty = 1:2, bty = "n")
if(requireNamespace("mirt")) {
## fit 2PL to verbal aggression data
twoplmod <- plmodel(VerbalAggression$resp2)
## category information plots for all items under the dichotomous 2PL
plot(twoplmod, type = "information", what = "categories")
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