Profile Plots for IRT Models
Base graphics plotting function for profile plot visualization of IRT models.
profileplot(object,
what = c("items", "thresholds", "discriminations", "guessings", "uppers"),
parg = list(type = NULL, ref = NULL, alias = TRUE, logit = FALSE), index = TRUE,
names = TRUE, main = NULL, abbreviate = FALSE, ref = TRUE,
col = "lightgray", border = "black", pch = NULL, cex = 1,
refcol = "lightgray", linecol = "black", lty = 2, ylim = NULL,
xlab = NULL, ylab = NULL, add = FALSE, srt = 45, adj = c(1.1, 1.1),
axes = TRUE, ...)object |
a fitted model object of class |
what |
character, specifying the type of parameters to be plotted. |
parg |
list of arguments passed over to internal calls of
|
index |
logical, should different indexes for different items be used? |
names |
logical or character. If |
main |
character, specifying the overall title of the plot. |
abbreviate |
logical or numeric, specifying whether object names are to be abbreviated. If numeric this controls the length of the abbreviation. |
ref |
logical, whether to draw a horizontal line for the reference level.
Only takes effect if argument |
col, border, pch, cex |
graphical appearance of plotting symbols. Can be
of the same length as the number of items, i.e., a different graphical
appearance is used for each item. If |
refcol |
character, specifying the line color for the reference line
(if |
linecol |
character or numeric, specifying the line color to be used for the profiles. |
lty |
numeric, specifying the line type for the profiles. |
ylim |
numeric, specifying the y axis limits. |
xlab, ylab |
character, specifying the x and y axis labels. |
add |
logical. If |
srt, adj |
numeric. Angle ( |
axes |
logical. Should axes be drawn? |
... |
further arguments passed over to |
The profile plot visualization illustrates profiles of specific estimated parameters under a certain IRT model.
## 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$resp)
## profile plots of the item parameters of the three fitted IRT models
plot(rmmod, type = "profile", what = "items", col = 4)
plot(rsmod, type = "profile", what = "items", col = 2, add = TRUE)
plot(pcmod, type = "profile", what = "items", col = 3, add = TRUE)
legend(x = "topleft", legend = c("RM", "RSM", "PCM"), col = 1,
bg = c(4, 2, 3), pch = 21, bty = "n")
## profile plots of the threshold parameters of type "mode"
plot(rmmod, type = "profile", what = "thresholds", parg = list(type = "mode"))
plot(rsmod, type = "profile", what = "thresholds", parg = list(type = "mode"))
plot(pcmod, type = "profile", what = "thresholds", parg = list(type = "mode"))
## profile plot of the discrimination parameters of the dichotomous RM
plot(rmmod, type = "profile", what = "discrimination")
if(requireNamespace("mirt")) {
## fit 2PL and generalized partial credit model to verbal aggression data
twoplmod <- plmodel(VerbalAggression$resp2)
gpcmod <- gpcmodel(VerbalAggression$resp)
## profile plot of the discrimination parameters of a dichotomous 2PL
plot(twoplmod, type = "profile", what = "discrimination")
## profile plot of the item parameters of the 2PL and GPCM
plot(twoplmod, type = "profile", what = "items", col = 4)
plot(gpcmod, type = "profile", what = "items", col = 2, add = TRUE)
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