R: Information Plots for IRT Models

infoplot {psychotools} | R Documentation

## Information Plots for IRT Models

### Description

Base graphics plotting function for information plot visualization of IRT models.

### Usage

      infoplot(object, what = c("categories", "items", "test"),
        ref = NULL, items = NULL, names = NULL, layout = NULL,
        xlim = NULL, ylim = NULL, col = NULL, lty = NULL, lwd = NULL,
        main = NULL, legend = TRUE, xlab = "Latent trait",
        ylab = "Information", add = FALSE, ...)

### Arguments

`object` | a fitted model object of class `"raschmodel"`, `"rsmodel"` or `"pcmodel"`.
`what` | character, specifying the type of information to visualize.
`ref` | argument passed over to internal calls of `predict`.
`items` | character or numeric, specifying the items for which information curves should be visualized.
`names` | character, specifying labels for the items.
`layout` | matrix, specifying how the item or category information curves of different items should be arranged. If `null` and `what` is set to ```items''`, the item information curves are overlayed within a single plot.
`xlim, ylim` | numeric, specifying the x and y axis limits.
`col` | character, specifying the colors of the test, item or category information curves.
`lty` | numeric, specifying the line type of the information curves.
`lwd` | numeric, specifying the line width of the information curves.
`main` | character, specifying the overall title of the plot.
`legend` | logical, specifying if a legend is drawn when multiple item information curves are overlayed. The labels in the legend correspond to the item names (which can be specified in the argument `names`).
`xlab, ylab` | character, specifying the x and y axis labels.
`add` | logical. If `TRUE`, new information curves are added to an existing plot. Only possible for a test or a single item information curve.
`...` | further arguments passed to internal calls of `matplot`

### Details

The information plot visualization illustrates the test, item or category information as a function of the ability parameter θ under a certain IRT model. Further details on the computation of the displayed information can be found on the help page of the function `predict.pcmodel`.

### See Also

`curveplot`, `regionplot`, `profileplot`, `piplot`

### Examples

    ## Load Verbal Aggression data
    data("VerbalAggression", package = "psychotools")

    ## Fit Rasch and partial credit
    ## model to Verbal Aggression data
    rmmod <- raschmodel(VerbalAggression$resp2)
    pcmod <- pcmodel(VerbalAggression$resp)

    ## Category information plots for all items under
    ## the dichotomous Rasch model
    plot(rmmod, type = "information", what = "categories")

    ## Category information plots for all items under
    ## the partial credit model
    plot(pcmod, type = "information", what = "categories")

    ## Overlayed item information plots for the first six
    ## item of the Verbal Aggression data set under
    ## the partial credit model
    plot(pcmod, type = "information", what = "items",
      items = 1:6)

    ## A comparison of the item information for the first six
    ## items under the dichotomous Rasch and the partial credit model
    plot(pcmod, type = "information", what = "items",
      items = 1:6, xlim = c(-5, 5))
    plot(rmmod, type = "information", what = "items",
      items = 1:6, lty = 2, add = TRUE)
    legend(x = "topright", legend = c("PCM", "RM"), lty = 1:2, bty = "n")

    ## A comparison of the test information based on all items
    ## of the Verbal Aggression data set under the dichotomous Rasch
    ## and the partial credit model
    plot(pcmod, type = "information", what = "test",
      items = 1:6, xlim = c(-5, 5))
    plot(rmmod, type = "information", what = "test",
      items = 1:6, lty = 2, add = TRUE)
    legend(x = "topright", legend = c("PCM", "RM"), lty = 1:2, bty = "n")

[Package psychotools version 0.4-2 Index]