Psychometric Properties of Scale Scores and Performance Levels for Performance Assessments Using Polytomous IRT

With a focus on performance assessments, this paper describes procedures for calculating conditional standard error of measurement (CSEM) and reliability of scale scores and classification consistency of performance levels. Scale scores that are transformations of total raw scores are the focus of these procedures, although other types of raw scores are considered as well. Polytomous IRT models provide the psychometric foundation for the procedures that are described. The procedures are applied using test data from ACT's Work Keys Writing Assessment to demonstrate their usefulness. Two polytomous IRT models were compared, as were two different procedures for calculating scores. One simulation study was done using one of the models to evaluate the accuracy of the proposed procedures. The results suggest that the procedures provide quite stable estimates and have the potential to be useful in a variety of performance assessment situations.