mirt (version 0.1-19)

itemplot: Displays item surface and information plots

Description

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

Usage

itemplot(object, item, ...)

## S3 method for class 'mirt':
itemplot(object, item, type = 'info',
  npts = 50, rot = list(x = -70, y = 30, z = 10), ...)

## S3 method for class 'bfactor':
itemplot(object, item, type = 'info',
  npts = 50, rot = list(x = -70, y = 30, z = 10), ...)

## S3 method for class 'polymirt':
itemplot(object, item, type = 'info',
  npts = 50, rot = list(x = -70, y = 30, z = 10), ...)

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 contour plot. Not

npts

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

rot

allows rotation of the 3D graphics

...

additional arguments to be passed

See Also

plot

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))