Alternative Linear Item Response Theory Observed-Score Equating Methods

Item response theory observed-score equating (IRTOSE) is widely used in many testing programs. The aim of this study was to empirically examine three alternative linear IRTOSE methods compared with the traditional IRTOSE method and to discuss these methods in light of previously suggested alternatives. This contribution is both conceptual, by exploring three alternative methods that fit into the current observed-score equating framework, and empirical by comparing the methods through simulations and with real data. The results show that the local linear (kernel) IRTOSE methods yield low bias and low values on loss measures. However, using only a linear IRTOSE method results in excessive bias and cannot be recommended because of the ease with which IRTOSE with full distributions can be performed. An example using real data showed considerable differences in the equated scores with the alternative methods as well as in comparison with the traditional IRTOSE method. Practical considerations are given in the concluding remarks.