plot.lordif: Plot method for lordif class

In lordif: Logistic Ordinal Regression Differential Item Functioning using IRT

Description

plots diagnostic graphs for items flagged for DIF

Usage

  ## S3 method for class 'lordif'
plot(x, labels = c("Reference", "Focal"), width = 7, height = 7, ...)

Arguments

x	output from lordif
labels	labels for group levels, e.g., c("Male","Female")
width	width of the canvas of the plotting device in inches
height	height of the canvas of the plotting device in inches
...	extra graphical parameters

Details

Generates the following graphs IF there is one or more DIF items: 1. Trait Distributions - density graphs for groups 2. Item True Score Functions - true score functions by theta for groups 3. Differences in Item True Score Functions - unsigned differences 4. Item Response Functions - item response function for groups 5. Impact (Weighted by Density) - unsigned differences weighted by theta distributions for the focal group 6. Comparison of TCCs by group based on all items and DIF items 7. Impact on Theta Estimates - theta estimates by group before and after accounting for DIF

Graphs 2-5 are generated for each DIF item Graphs 1, 6 and 7 are generated for the whole analysis

Value

Returns no object.

Note

Produces graphs only if x contains DIF items. No graphs if no DIF items are present.

Author(s)

Seung W. Choi <[e-mail]>

References

Choi, S. W., Gibbons, L. E., Crane, P. K. (2011). lordif: An R Package for Detecting Differential Item Functioning Using Iterative Hybrid Ordinal Logistic Regression/Item Response Theory and Monte Carlo Simulations. Journal of Statistical Software, 39(8), 1-30. URL http://www.jstatsoft.org/v39/i08/.

See Also

lordif

Examples

##run lordif first
## Not run: age.dif <- lordif(Anxiety[paste("R",1:29,sep="")],Anxiety$age)
## Not run: plot(age.dif,labels=c("Younger","Older"),width=8,height=7,cex=0.8,lwd=1)

Example output

Loading required package: mirt
Loading required package: stats4
Loading required package: lattice
Loading required package: rms
Loading required package: Hmisc
Loading required package: survival
Loading required package: Formula
Loading required package: ggplot2

Attaching package: 'Hmisc'

The following objects are masked from 'package:base':

    format.pval, units

Loading required package: SparseM

Attaching package: 'SparseM'

The following object is masked from 'package:base':

    backsolve

lordif documentation built on May 2, 2019, 2:13 p.m.