Comparison of Rasch Preequating and Postequating When Item Parameters Drift

Test equating is commonly applied in psychological and educational assessments to ensure score comparability across multiple test forms. However, item parameter drift (IPD) poses a threat to equating, potentially impacting the validity, fairness, and reliability of test scores. This study investigates the effects of IPD on true-score preequating and postequating within the Rasch framework, commonly used in certification and licensure testing programs. Through a simulation study, we examined various scenarios, including IPD direction, percentage of items exhibiting IPD, magnitude of IPD, and examinee sample size. Our findings indicate that postequating consistently outperforms preequating in the presence of IPD, demonstrating greater robustness in maintaining equating accuracy and fairness. The results highlight the importance of considering IPD in equating processes and suggest that postequating may be preferable in contexts where IPD occurs. These insights are valuable for test practitioners managing assessments susceptible to IPD, ensuring more accurate and reliable score interpretations.