eRm (version 0.15-5)

plotPWmap: Pathway Map

Description

A Bond-and-Fox Pathway Map displays the location of each item or each person against its infit t-statistic. Pathway maps are useful for identifying misfitting items or misfitting persons. Items or people should ideally have a infit t-statistic lying between about -2 and +2, and these values are marked.

Usage

plotPWmap(object, pmap = FALSE, imap=TRUE,
                 item.subset = "all", person.subset = "all",
                 mainitem = "Item Map", mainperson = "Person Map",
                 mainboth="Item/Person Map",
                 latdim = "Latent Dimension",
                 tlab = "Infit t statistic",
                 pp = NULL, cex.gen = 0.6, cex.pch=1,
                 person.pch = 1, item.pch = 16,
                 personCI = NULL, itemCI = NULL, horiz=FALSE)

Arguments

object

Object of class Rm or dRm

pmap

Plot a person map if TRUE; the default is FALSE.

imap

Plot an item map if TRUE (the default); do not plot if FALSE. At least one of pmap and imap must be TRUE.

item.subset

Subset of items to be plotted for an item map. Either a numeric vector indicating the item numbers or a character vector indicating the item names. If "all", all items are plotted. The number of items to be plotted must be > 1

person.subset

Subset of persons to be plotted for a person map. Either a numeric vector indicating the person numbers or a character vector indicating the person names. If "all", all persons are plotted. The number of persons to be plotted

mainitem

Main title of an item plot.

mainperson

Main title of a person plot.

mainboth

Main title of a person/item joint plot.

latdim

Label of the y-axis, i.e., the latent dimension.

tlab

Label of the x-axis, i.e., the t-statistic dimension.

pp

If non-NULL, this contains the person.parameter data of the data object, avoiding the need to recalculate it.

cex.gen

cex as a graphical parameter specifies a numerical value giving the amount by which plotting text and symbols should be magnified relative to the default. Here cex.gen applies to all text labels. The default i

cex.pch

applies to all plotting symbols. The default is 1.

person.pch, item.pch

Specifies the symbol used for plotting person data and item data respectively; the defaults are 1 and 16 respectively. See points for more information about pch values.

personCI, itemCI

Plotting confidence intervals for the the person abilities and item difficulties. If personCI=NULL (the default) no confidence intervals are drawn for person abilities. Otherwise, specifying personCI draws a

horiz

if TRUE, the plot is horizontal, i.e., the latent dimension is on the x-axis. The default is FALSE.

encoding

UTF-8

Details

This code uses vertical(horizontal) error bars rather than circles or boxes to indicate standard errors. It also offers the possibility of plotting item or person data on its own; this can considerably simplify the reading of the plots for large datasets.

References

Bond T.G., Fox C.M. (2007) Applying the Rasch Model: Fundamental Measurement in the Human Sciences (2nd ed.) chapter 3, Lawrence Erlbaum Associates, Inc. Linacre J.M., Wright B.D. (1994) Dichotomous Infit and Outfit Mean-Square Fit Statistics / Chi-Square Fit Statistics. Rasch Measurement Transactions 8:2 p. 350, http://www.rasch.org/rmt/rmt82a.htm Linacre J.M. (2002) What do Infit and Outfit, Mean-square and Standardized mean? Rasch Measurement Transactions 16:2 p. 878, http://www.rasch.org/rmt/rmt162f.htm Wright B.D., Masters G.N. (1990) Computation of OUTFIT and INFIT Statistics. Rasch Measurement Transactions 3:4 p. 84--85, http://www.rasch.org/rmt/rmt34e.htm

Examples

res <- PCM(pcmdat)
pparm <- person.parameter(res)
plotPWmap(res, pp = pparm)
plotPWmap(res, pp = pparm, pmap = TRUE)