plotPWmap function

Pathway Map

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. UTF-8

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 must be > 1.

• 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 is 0.6.

• 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 approximate confidence intervals for each person's ability. personCI must be specified as a list, and the optional elements of this list are gamma, the confidence level, col, colour, and lty, line type. If personCI

  is specified as an empty list, or not all of the list items are specified, the default values personCI=list(gamma=0.95,col="orange",lty="dotted") will be used.

  The same goes for itemCI, except that the default settings are itemCI=list(gamma=0.95,col="red",lty="dotted").

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

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, https://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, https://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, https://www.rasch.org/rmt/rmt34e.htm

Author(s)

Julian Gilbey

Examples

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