Innovations in Measuring Rater Accuracy in Standard Setting: Assessing “Fit” to Item Characteristic Curves

摘要

Standard setting methods such as the Angoff method rely on judgments of item characteristics; item response theory empirically estimates item characteristics and displays them in item characteristic curves (ICCs). This study evaluated several indexes of rater fit to ICCs as a method for judging rater accuracy in their estimates of expected item performance for target groups of test-takers. Simulated data were used to compare adequately fitting ratings to poorly fitting ratings at various target competence levels in a simulated two stage standard setting study. The indexes were then applied to a set of real ratings on 66 items evaluated at 4 competence thresholds to demonstrate their relative usefulness for gaining insight into rater “fit.” Based on analysis of both the simulated and real data, it is recommended that fit indexes based on the absolute deviations of ratings from the ICCs be used, and those based on the standard errors of ratings should be avoided. Suggestions are provided for using these indexes in future research and practice.