plotPImap: Person-Item Map

In eRm: Extended Rasch Modeling

Person-Item Map

Description

A person-item map displays the location of item (and threshold) parameters as well as the distribution of person parameters.along the latent dimension. Person-item maps are useful to compare the range and position of the item measure distribution (lower panel) to the range and position of the person measure distribution (upper panel). Items should ideally be located along the whole scale to meaningfully measure the ‘ability’ of all persons.

Usage

plotPImap(object, item.subset = "all", sorted = FALSE,
   main = "Person-Item Map", latdim = "Latent Dimension",
   pplabel = "Person\nParameter\nDistribution", cex.gen = 0.7,
   xrange = NULL, warn.ord = TRUE, warn.ord.colour = "black",
   irug = TRUE, pp = NULL)

Arguments

object	Object of class Rm or dRm
item.subset	Subset of items to be plotted. Either a numeric vector indicating the column in X or a character vector indicating the column name. If "all", all items are plotted. The number of items to be plotted must be > 1.
sorted	If TRUE, the items are sorted in increasing order according to their location on the latent dimension.
main	Main title of the plot.
latdim	Label of the x-axis, i.e., the latent dimension.
pplabel	Title for the upper panel displaying the person parameter distribution
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 0.7.
xrange	Range for the x-axis
warn.ord	If TRUE (the default) asterisks are displayed in the right margin of the lower panel to indicate nonordinal threshold locations for polytomous items.
warn.ord.colour	Nonordinal threshold locations for polytomous items are coloured with this colour to make them more visible. This is especially useful when there are many items so that the plot is quite dense. The default is "black", so that there is no distinction made.
irug	If TRUE (the default), all thresholds are plotted below the person distribution to indicate where the included items are most informative.
pp	If non-NULL, this contains the person.parameter data of the data object, avoiding the need to recalculate it.

Details

Item locations are displayed with bullets, threshold locations with circles.

Author(s)

Patrick Mair, Reinhold Hatzinger, patches from Julian Gilbey and Marco J. Maier

References

Bond, T.G., and Fox Ch.M. (2007) Applying the Rasch Model. Fundamental Measurement in the Human Sciences. 2nd Edition. Lawrence Erlbaum Associates.

Examples

res <- PCM(pcmdat)
plotPImap(res, sorted=TRUE)

eRm documentation built on May 29, 2024, 2:12 a.m.