R: Profile Plots for IRT Models

profileplot {psychotools} | R Documentation

## Profile Plots for IRT Models

### Description

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

### Usage

      profileplot(object, what = c("items", "thresholds", "discriminations"),
        parg = list(type = NULL, ref = NULL, alias = TRUE),
        index = TRUE, names = TRUE, main = NULL, abbreviate = FALSE,
        ref = TRUE, col = "lightgray", border = "black", pch = NULL, cex = 1,
        refcol = "lightgray", linecol = "black", lty = 2, ylim = NULL,
        xlab = NULL, ylab = NULL, add = FALSE, srt = 45, adj = c(1.1, 1.1),
        axes = TRUE, ...)

### Arguments

`object` | a fitted model object of class `"raschmodel"`, `"rsmodel"` or `"pcmodel"`.
`what` | character, specifying the type of parameters to be plotted.
`parg` | list of arguments passed over to internal calls of `itempar`, `threshpar` or `discrpar`.
`index` | logical, should different indexes for different items be used?
`names` | logical or character. If `TRUE`, the names of the items are displayed on the x-axis. If `FALSE`, numbers of items are shown. Alternatively a character vector of the same length as the number of items can be supplied.
`main` | character, specifying the overall title of the plot.
`abbreviate` | logical or numeric, specifying whether object names are to be abbreviated. If numeric this controls the length of the abbreviation.
`ref` | logical, whether to draw a horizontal line for the reference level. Only takes effect if argument `what` is `"items"` or `"discriminations".`
`col, border, pch, cex` | Graphical appearance of plotting symbols. Can be of the same length as the number of items, i.e., a different graphical appearance is used for each item. If `what = "thresholds"`, `col` and `pch` can be matrices with a number of columns equal to the number of threshold parameters per item resulting in different symbols and colors used for different threshold parameter profiles.
`refcol` | character, specifying the line color for the reference line (if `ref`).
`linecol` | character or numeric, specifying the line color to be used for the profiles.
`lty` | numeric, specifying the line type for the profiles.
`ylim` | numeric, specifying the y axis limits.
`xlab, ylab` | character, specifying the x and y axis labels.
`add` | logical. If `TRUE`, new plotted profiles are added to an existing plot.
`srt, adj` | numeric. Angle (`srt`) and adjustment (`adj`) in case names (rather than numbers) are used as x-axis labels. These are passed to `text`.
`axes` | logical. Should axes be drawn?
`...` | further arguments passed over to `plot`.

### Details

The profile plot visualization illustrates profiles of specific estimated parameters under a certain IRT model.

### See Also

`curveplot`, `regionplot`, `infoplot`, `piplot`

### Examples

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

    ## Fit Rasch, rating scale and partial credit
    ## model to VerbalAggression data
    rmmod <- raschmodel(VerbalAggression$resp2)
    rsmod <- rsmodel(VerbalAggression$resp)
    pcmod <- pcmodel(VerbalAggression$resp)

    ## Profile plots of the item parameters of
    ## the three fitted IRT models
    plot(rmmod, type = "profile", what = "items", col = 4)
    plot(rsmod, type = "profile", what = "items", col = 2, add = TRUE)
    plot(pcmod, type = "profile", what = "items", col = 3, add = TRUE)
    legend(x = "topleft", legend = c("RM", "RSM", "PCM"),
      col = 1, bg = c(4, 2, 3), pch = 21, bty = "n")

    ## Profile plots of the threshold parameters of type 'mode'
    plot(rmmod, type = "profile", what = "thresholds",
      parg = list(type = "mode"))
    plot(rsmod, type = "profile", what = "thresholds",
      parg = list(type = "mode"))
    plot(pcmod, type = "profile", what = "thresholds",
      parg = list(type = "mode"))

    ## Profile plot of the discrimination parameters
    ## of a dichotomous Rasch model (all zero by definition)
    plot(rmmod, type = "profile", what = "discrimination")

[Package psychotools version 0.4-2 Index]