node_regionplot function

Panel-Generating Function for Visualizing IRT Tree Models

Panel-generating function for visualizing the regions of expected item responses across abilities (via shaded rectangles) based on the parameters from the nodes in IRT tree models.

node_regionplot(
  mobobj,
  names = FALSE,
  abbreviate = TRUE,
  type = c("mode", "median", "mean"),
  ref = NULL,
  ylim = NULL,
  off = 0.1,
  col_fun = gray.colors,
  bg = "white",
  uo_show = TRUE,
  uo_col = "red",
  uo_lty = 2,
  uo_lwd = 1.25,
  ylines = 2
)

Arguments

• mobobj: an object of class "npltree" or class "mob"

  fitted by npltree

• 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.

• abbreviate: logical. Should item names be abbreviated? If numeric this controls the length of the abbreviation.

• type: character, specifying which type of threshold parameters are to be used to mark the category regions per item in the plot (see regionplot for details).

• ref: a vector of labels or position indices of item parameters which should be used as restriction/for normalization. If NULL (the default), all items are used (sum zero restriction). See threshpar for more details.

• ylim: y axis limits

• off: numeric, the distance (in scale units) between two item rectangles.

• col_fun: function. Function to use for creating the color palettes for the rectangles. Per default gray.colors is used. Be aware that col_fun should accept as first argument an integer specifying the number of colors to create.

• bg: color for background filling.

• uo_show: logical. If set to TRUE (the default), disordered absolute item threshold parameters are indicated by a horizontal line (only if type is set to "mode").

• uo_col: character, color of indication lines (if uo_show).

• uo_lty: numeric. Line typ of indication lines (if uo_show).

• uo_lwd: numeric. Line width of indication lines (if uo_show).

• ylines: numeric. Number of lines used for y-axis labels.

Returns

A panel function which can be supplied to the plot method for "npltree" objects or "mob" objects fitted by npltree.