plot.lordif {lordif} | R Documentation |
Plot method for lordif class
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 |
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
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)