Detecting and Correcting Scale Drift in Test Equating: An Illustration from a Large Scale Testing Program

The purpose of this study is to determine the extent of scale drift on a test that employs cut scores. It was essential to examine scale drift for this testing program because new forms in this testing program are often put on scale through a series of intermediate equatings (known as equating chains). This process may cause equating error to accumulate to a point when scale scores are rendered incomparable across two parallel chains or time periods. The study examined two conditions (i.e., parallel equating chains or a single long chain) to evaluate whether scale drift occurred for these conditions. Data from three tests that employed cut scores were used in this study. Results indicated that although there were some differences observed between the actual equating conversions derived via different equating chains, the effect of these differences on actual pass and fail status of test takers was not large. Recommendations on some alternatives to follow when a scale drift is observed are made and implications for future research are discussed.