R: Person-Item Plots for IRT Models

piplot {psychotools} | R Documentation

## Person-Item Plots for IRT Models

### Description

Base graphics plotting function for person-item plot visualization of IRT models.

### Usage

      piplot(object, ref = NULL, items = NULL, xlim = NULL, names = NULL,
        labels = TRUE, main = "Person-Item Plot", xlab = "Latent trait",
        abbreviate = FALSE, cex.axis = 0.8, cex.text = 0.5, cex.points = 1.5, ...)

### Arguments

`object` | a fitted model object of class `"raschmodel"`, `"rsmodel"` or `"pcmodel"`.
`ref` | argument passed over to internal calls of `threshpar` and `itempar`.
`items` | character or numeric, specifying the items which should be visualized in the person-item plot.
`xlim` | numeric, specifying the x axis limits.
`names` | character, specifying labels for the items.
`labels` | logical, whether to draw the number of the threshold as text below the threshold.
`main` | character, specifying the overall title of the plot.
`xlab` | character, specifying the x axis labels.
`abbreviate` | logical or numeric, specifying whether object names are to be abbreviated. If numeric this controls the length of the abbreviation.
`cex.axis` | numeric, the magnification to be used for the axis notation relative to the current setting of `cex`.
`cex.text` | numeric, the magnification to be used for the symbols relative to the current setting of `cex`.
`cex.points` | numeric, the magnification to be used for the points relative to the current setting of `cex`.
`...` | further arguments passed to internal calls of `lines`, `points` and `text`

### Details

The person-item plot visualization illustrates the distribution of the person parameters against the absolute item threshold parameters under a certain data set and IRT model.

### See Also

`curveplot`, `regionplot`, `profileplot`, `infoplot`

### Examples

    ## Verbal aggression data
    data("VerbalAggression", package = "psychotools")

    ## Fit a partial credit model to VerbalAggression data
    pcmod <- pcmodel(VerbalAggression$resp)

    ## Create a person-item plot visualization of the fitted PCM
    plot(pcmod, type = "piplot")

    ## Just visualize the first six items
    plot(pcmod, type = "piplot", ref = 1:6)

[Package psychotools version 0.4-2 Index]