Response Curve Plots for IRT Models
Base graphics plotting function for response curve plot visualization of IRT models.
curveplot(object, ref = NULL, items = NULL, names = NULL,
layout = NULL, xlim = NULL, ylim = c(0, 1), col = NULL,
lty = NULL, main = NULL, xlab = "Latent trait",
ylab = "Probability", add = FALSE, ...)object |
a fitted model object of class |
ref |
argument passed over to internal calls of |
items |
character or numeric, specifying the items for which response curves should be visualized. |
names |
character, specifying labels for the items. |
layout |
matrix, specifying how the response curve plots of different items should be arranged. |
xlim, ylim |
numeric, specifying the x and y axis limits. |
col |
character, specifying the colors of the response curve lines. The
length of |
lty |
numeric, specifying the line type of the response curve lines. The
length of |
main |
character, specifying the overall title of the plot. |
xlab, ylab |
character, specifying the x and y axis labels. |
add |
logical. If |
... |
further arguments passed to internal calls of
|
The response curve plot visualization illustrates the predicted probabilities as a function of the ability parameter θ under a certain IRT model. This type of visualization is sometimes also called item/category operating curves or item/category characteristic curves.
## load verbal aggression data
data("VerbalAggression", package = "psychotools")
## fit Rasch, rating scale and partial credit model to verbal aggression data
rmmod <- raschmodel(VerbalAggression$resp2)
rsmod <- rsmodel(VerbalAggression$resp)
pcmod <- pcmodel(VerbalAggression$resp)
## curve plots of the dichotomous RM
plot(rmmod, type = "curves")
## curve plots under the RSM for the first six items of the data set
plot(rsmod, type = "curves", items = 1:6)
## curve plots under the PCM for the first six items of the data set with
## custom labels
plot(pcmod, type = "curves", items = 1:6, names = paste("Item", 1:6))
## compare the predicted probabilities under the RSM and the PCM for a single
## item
plot(rsmod, type = "curves", item = 1)
plot(pcmod, type = "curves", item = 1, lty = 2, add = TRUE)
legend(x = "topleft", y = 1.0, legend = c("RSM", "PCM"), lty = 1:2, bty = "n")
if(requireNamespace("mirt")) {
## fit 2PL and generaliced partial credit model to verbal aggression data
twoplmod <- plmodel(VerbalAggression$resp2)
gpcmod <- gpcmodel(VerbalAggression$resp)
## curve plots of the dichotomous 2PL
plot(twoplmod, type = "curves", xlim = c(-6, 6))
## curve plots under the GPCM for the first six items of the data set
plot(gpcmod, type = "curves", items = 1:6, xlim = c(-6, 6))
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