mirt (version 0.2.1)

itemplot: Displays item surface and information plots

Description

itemplot displays 3D surface plots if the number of factors is two, or standard 2D plots if the number of factors is equal to one.

Arguments

object

a computed model of class bfactorClass, mirtClass, or polymirtClass

item

a single numerical value indicating which item to plot

type

type of graphic to plot, may be either 'curve' for the response surface curve, 'info' for the item information, 'contour' for item probability contours, or 'infocontour' for information conto

npts

number of points to use per dimension. A higher value will make the graphs look smoother. Default is 50

rot

allows rotation of the 3D graphics. Default is list(x=-70,y=30,z=10)

...

additional arguments to be passed

See Also

plot, mirt, bfactor, polymirt

Examples

data(LSAT7)
fulldata <- expand.table(LSAT7)
mod1 <- mirt(fulldata,1)
mod2 <- mirt(fulldata,2)

#first item unidimensional
itemplot(mod1, 1)
itemplot(mod1, 1, type = 'info')

#first item multidimensional
itemplot(mod2, 1)
itemplot(mod2, 1, type = 'info')
#turn it a little
itemplot(mod2, 1, type = 'info', rot = list(x = -70, y = -15, z = -10))