lordif (version 0.3-3)

plot.lordif: Plot method for lordif class

Description

plots diagnostic graphs for items flagged for DIF

Usage

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

Value

Returns no object.

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

Author

Seung W. Choi <[e-mail]>

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

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
if (FALSE) age.dif <- lordif(Anxiety[paste("R",1:29,sep="")],Anxiety$age)
if (FALSE) plot(age.dif,labels=c("Younger","Older"),width=8,height=7,cex=0.8,lwd=1)