Equating designs and procedures used in Rasch scaling

The development of alternate forms of tests requires a statistical score adjustment called equating that permits the interchanging of scores from different test forms. Equating makes possible several important measurement applications, including removing practice effects in pretest-posttest research designs, improving test security, comparing scores between new and old forms, and supporting item bank development for computerized adaptive testing. This article summarizes equating methods from a Rasch measurement perspective. The four sections of this article present an introduction and definition of equating and related linking methods, data collection designs, equating procedures, and evaluating equated measures. The methods are illustrated with worked examples.