Modeling and Multivariate Methods - SAS

Chapter 22 Scoring Tests Using Item Response Theory 531
Item Analysis Output
Figure 22.9 Elements of the ICC Display
ICC
Information
Curve
ICC Inflection Point
Information Curves
Questions provide varying levels of information for different ability levels. The gray information curves for
each item show the amount of information that each question contributes to the total information of the
test. The total information of the test for the entire range of abilities is shown in the Information Plot
section of the report (Figure 22.10).
Figure 22.10 Information Plot
Dual Plots
The information gained from item difficulty parameters in IRT models can be used to construct an
increasing scale of questions, from easiest to hardest, on the same scale as the examinees. This structure gives
information on which items are associated with low levels of the trait, and which are associated with high
levels of the trait.
JMP shows this correspondence with a dual plot. The dual plot for this example is shown in Figure 22.11.