lordif (version 0.1-1)

plotDIF: plots DIF graphs for flagged items

Description

plots diagnostic graphs for items identified as displaying DIF

Usage

plotDIF(obj, labels = c("Reference", "Focal"), cexp = 0.8)

Arguments

obj

output from lordif

labels

labels for group levels, e.g., c("Male","Female")

cexp

character expansion factor, e.g., cexp=2 for two times a normal size

Value

• Returns no object.

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. (April, 2009). Development of freeware for an iterative hybrid ordinal logistic regression/IRT DIF. Paper Presented at the National Council of Measurement in Education. San Diego, CA.

See Also

lordif

Examples

##run lordif first
age.dif <- lordif(Anxiety[paste("R",1:29,sep="")],Anxiety$age)
plotDIF(age.dif,labels=c("Younger","Older"))