rim function

Item-total regressions for the Rasch vs. the interaction model

Compare the item-total regressions fit by the Rasch model and the interaction model, for one, several, or all items in the test.

rim(x, items = NULL, showData = FALSE, shade = 10, ncol = 3, ...)

Arguments

• x: A matrix of scored responses (persons in rows, items in columns)

• items: The items to plot (column numbers). If NULL, all items will be plotted

• showData: If TRUE, the observed proportion correct at each sum score will be shown on the plot. Default is FALSE (show only the regressions)

• shade: The part of the probability mass for the sum scores to shade out, shown as percentage. Default is 10: shade the most extreme 10

  Ignored when add=TRUE.

• ncol: When plotting multiple items, the user can suggest the number of columns in the matrix of plots (up to 3, will be adjusted if necessary)

• ...: Any additional plotting parameters

Examples

rim(Scored, items=2)

See Also

interactionModel

Author(s)

Ivailo Partchev, using theory and C code by Gunter Maris