mokken (version 1.2)

plot.pmatrix.class: Plot pmatrix.class objects

Description

S3 Method to plot objects of class pmatrix.class. Graphic display of the checks of pmatrix. One graph for each item plotting the rows of the P(++) matrix and rows of the P(--) matrix. If nonintersection holds the lines in the plots of the P(++) matrix must be nondecreasing and the lines in the plots of the P(--) matrix nust be nonincreasing.

Usage

## S3 method for class 'pmatrix.class':
plot(x, items = all, pmatrix="both", ...)

Arguments

x

Object of class pmatrix.class produced by check.pmatrix.

items

vector containing the numbers of the item pairs for which the results are depicted graphically. Default the results for all items are depicted.

pmatrix

Valid options are "ppp", "pmm", and "both". If pmatrix="ppp", then the P(++) matrix is plotted, if pmatrix="pmm", then the P(--) matrix is plotted, if pmatrix="both"

...

Optional graphical parameters will be ignored

Value

• Returns a graph.

Details

The default graphic device in R may only display the last graph. In the plot of the P(++) matrix and the P(--) matrix, the x-axis contains the $k =(J-1)m$ item steps not pertaining to item j in order of popularity (ascending). Let $Y_g=1$ indicate that the g-th item step has been taken: i.e. $Xi \geq y$ and let $Y_g=0$ indicate that the g-th item step has not been taken: i.e. $Xi < y$. The $m$ lines in the plot of the P(++) matrix connect $P(X_j \geq x, Y_1=1), \dots, P(X_j \geq x, Y_k=1)), x = 1, \dots m$. The $m$ lines in the plot of the P(--) matrix connect $P(X_j < x, Y_1=0), \dots, P(X_j < x, Y_k=0)), x = 1, \dots, m$. If the number of item steps on the x-axis is greater than 10, then the labels are not displayed,

References

Molenaar, I.W. and Sijtsma, K. (2000) User's Manual MSP5 for Windows [Software manual]. Groningen, The Netherlands: IEC ProGAMMA. Sijtsma, K, and Molenaar, I. W. (2002) Introduction to nonparametric item response theory. Thousand Oaks, CA: Sage. Van der Ark, L. A. (2007). Mokken scale analysis in R. Journal of Statistical Software. http://www.jstatsoft.org

See Also

check.pmatrix, summary.pmatrix.class

Examples

data(acl)
pmatrix.list <- check.pmatrix(acl[,1:10])
plot(pmatrix.list)
summary(pmatrix.list)