mirt: itemplot – R documentation

Become an expert in R — Interactive courses, Cheat Sheets, certificates and more!

itemplot

Displays item surface and information plots

Description

itemplot displays various item based IRT plots, with special options for plotting items that contain several 0 slope parameters. Supports up to three dimensional models.

Usage

itemplot(
  object,
  item,
  type = "trace",
  degrees = 45,
  CE = FALSE,
  CEalpha = 0.05,
  CEdraws = 1000,
  drop.zeros = FALSE,
  theta_lim = c(-6, 6),
  shiny = FALSE,
  rot = list(xaxis = -70, yaxis = 30, zaxis = 10),
  par.strip.text = list(cex = 0.7),
  npts = 200,
  par.settings = list(strip.background = list(col = "#9ECAE1"), strip.border = list(col
    = "black")),
  auto.key = list(space = "right", points = FALSE, lines = TRUE),
  ...
)

Arguments

`object`	a computed model object of class `SingleGroupClass` or `MultipleGroupClass`. Input may also be a `list` for comparing similar item types (e.g., 1PL vs 2PL)
`item`	a single numeric value, or the item name, indicating which item to plot
`type`	plot type to use, information (`'info'`), standard errors (`'SE'`), item trace lines (`'trace'`), information and standard errors (`'infoSE'`) or information and trace lines (`'infotrace'`), relative efficiency lines (`'RE'`), expected score `'score'`, or information and trace line contours (`'infocontour'` and `'tracecontour'`; not supported for `MultipleGroupClass` objects)
`degrees`	the degrees argument to be used if there are two or three factors. See `iteminfo` for more detail. A new vector will be required for three dimensional models to override the default
`CE`	logical; plot confidence envelope?
`CEalpha`	area remaining in the tail for confidence envelope. Default gives 95% confidence region
`CEdraws`	draws number of draws to use for confidence envelope
`drop.zeros`	logical; drop slope values that are numerically close to zero to reduce dimensionality? Useful in objects returned from `bfactor` or other confirmatory models that contain several zero slopes
`theta_lim`	lower and upper limits of the latent trait (theta) to be evaluated, and is used in conjunction with `npts`
`shiny`	logical; run interactive display for item plots using the `shiny` interface. This primarily is an instructive tool for demonstrating how item response curves behave when adjusting their parameters
`rot`	a list of rotation coordinates to be used for 3 dimensional plots
`par.strip.text`	plotting argument passed to `lattice`
`npts`	number of quadrature points to be used for plotting features. Larger values make plots look smoother
`par.settings`	plotting argument passed to `lattice`
`auto.key`	plotting argument passed to `lattice`
`...`	additional arguments to be passed to `lattice` and `coef()`

Author(s)

Phil Chalmers rphilip.chalmers@gmail.com

References

Chalmers, R., P. (2012). mirt: A Multidimensional Item Response Theory Package for the R Environment. Journal of Statistical Software, 48(6), 1-29. doi: 10.18637/jss.v048.i06

Examples

## Not run: 

data(LSAT7)
fulldata <- expand.table(LSAT7)
mod1 <- mirt(fulldata,1,SE=TRUE)
mod2 <- mirt(fulldata,1, itemtype = 'Rasch')
mod3 <- mirt(fulldata,2)

itemplot(mod1, 2)
itemplot(mod1, 2, CE = TRUE)
itemplot(mod1, 2, type = 'info')
itemplot(mod1, 2, type = 'info', CE = TRUE)

mods <- list(twoPL = mod1, onePL = mod2)
itemplot(mods, 1, type = 'RE')

#multidimensional
itemplot(mod3, 4, type = 'info')
itemplot(mod3, 4, type = 'infocontour')
itemplot(mod3, 4, type = 'tracecontour')

#polytomous items
pmod <- mirt(Science, 1, SE=TRUE)
itemplot(pmod, 3)
itemplot(pmod, 3, CE = TRUE)
itemplot(pmod, 3, type = 'score')
itemplot(pmod, 3, type = 'infotrace')

# use the directlabels package to put labels on tracelines
library(directlabels)
plt <- itemplot(pmod, 3)
direct.label(plt, 'top.points')

# change colour theme of plots
bwtheme <- standard.theme("pdf", color=FALSE)
plot(pmod, type='trace', par.settings=bwtheme)
itemplot(pmod, 1, type = 'trace', par.settings=bwtheme)

# infoSE plot
itemplot(pmod, 1, type = 'infoSE')

# uncomment to run interactive shiny applet
# itemplot(shiny = TRUE)
    
## End(Not run)

mirt

Multidimensional Item Response Theory

v1.33.2

GPL (>= 3)

Authors

Phil Chalmers [aut, cre] (<https://orcid.org/0000-0001-5332-2810>), Joshua Pritikin [ctb], Alexander Robitzsch [ctb], Mateusz Zoltak [ctb], KwonHyun Kim [ctb], Carl F. Falk [ctb], Adam Meade [ctb], Lennart Schneider [ctb], David King [ctb], Chen-Wei Liu [ctb], Ogreden Oguzhan [ctb]

Initial release