## 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 <choi.phd@gmail.com>
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)