Parallel Tests & Equating: Theory, Principles, and Practice

Parallel Tests & Equating: Theory, Principles, and Practice

By Rojab Siti R. & Muhammad Yunus

Score equating is essential for any testing program that continually produces new editions of a test and for which the expectation is that scores from these editions have the same meaning over time. Different editions may be built to a common blueprint and be designed to measure the same constructs, but they almost invariably differ somewhat in their psychometric properties.

If one edition is more difficult than another, examinees would be expected to receive lower scores on the harder form. Score equating seeks to eliminate the effects on scores of these unintended differences in test form difficulty. Score equating is necessary to be fair to examinees and to provide score users with scores that mean the same thing across different editions or forms of the test.

Particularly in testing programs that help make high-stakes decisions, it is extremely important that test equating be done carefully and accurately. The reported scores, even though they represent the endpoint of a large test production, administration, and scoring enterprise, are the most visible part of a testing program. An error in the equating function or score conversion can affect the scores for all examinees, which is both a fairness and a validity concern. Because the reported score is so visible, the credibility of a testing organization hinges on activities associated with producing, equating, and reporting scores.

The term score linking is used to describe the transformation from a score on one test to a score on another test; score equating is a special type of score linking. There are different types of links, and the major difference between these types is not procedural, but interpretative. Holland and Dorans (2006) divided linking methods into three basic categories called predicting, scale aligning, and equating.