The purpose of this instructional module is to provide the basis for understanding the process of score equating through the use of item response theory (lRT). A context is provided for addressing the merits of IRT equating method. The mechanics of IRT equating and the need to place parameter estimates from separate calibration runs on the same scale are discussed. Some procedures for placing parameter estimates on a common scale are presented. In addition, IRT true-score equating is discussed in some detail. A discussion of the practical advantages derived from IRT equating is offered at the end of the module.

Keywords: calibration, equating, equating method, estimation, item response theory, IRT, parameter, scale, true-score equating