plotDIFirt {ShinyItemAnalysis} | R Documentation |
Plot item characteristic curve of DIF IRT model
Description
Plots characteristic curve of IRT model.
Usage
plotDIFirt(
parameters,
test = "Lord",
item = "all",
item.name,
same.scale = FALSE
)
Arguments
parameters |
numeric: data matrix or data frame. See Details. |
test |
character: type of statistic to be shown. See Details. |
item |
either character ("all"), or numeric vector, or single number corresponding to column indicators. See Details. |
item.name |
character: the name of item. |
same.scale |
logical: are the item |
Details
This function plots characteristic curve of DIF IRT model.
The parameters
matrix has a number of rows equal to twice the number
of items in the data set. The first J rows refer to the item parameter
estimates in the reference group, while the last J ones correspond to the
same items in the focal group. The number of columns depends on the selected
IRT model: 2 for the 1PL model, 5 for the 2PL model, 6 for the constrained
3PL model and 9 for the unconstrained 3PL model. The columns of
irtParam()
have to follow the same structure as the output of
itemParEst()
, difLord()
or difRaju()
command from the
difR
package.
Two possible type of test
statistics can be visualized - "Lord"
gives only characteristic curves, "Raju"
also highlights area between
these curves.
For default option "all"
, all characteristic curves are plotted.
Author(s)
Adela Hladka
Institute of Computer Science of the Czech Academy of Sciences
hladka@cs.cas.cz
Patricia Martinkova
Institute of Computer Science of the Czech Academy of
Sciences
martinkova@cs.cas.cz
See Also
difR::itemParEst()
, difR::difLord()
,
difR::difRaju()
Examples
# loading libraries
library(difR)
library(ltm)
# loading data based on GMAT2
data(GMAT2, package = "difNLR")
# Estimation of 2PL IRT model and Lord's statistic
# by difR package
fitLord <- difLord(GMAT2, group = 21, focal.name = 1, model = "2PL")
# plot of item 1 and Lord's statistic
plotDIFirt(fitLord$itemParInit, item = 1)
# Estimation of 2PL IRT model and Raju's statistic
# by difR package
fitRaju <- difRaju(GMAT2, group = 21, focal.name = 1, model = "2PL")
# plot of item 1 and Lord's statistic
plotDIFirt(fitRaju$itemParInit, test = "Raju", item = 1)