• Lawson DM

• Educational Measurement
• Models, Statistical

METHODS: The Rasch mathematical model (RMM) was selected from the family of IRT models because of its ability to work with smaller sample sizes. Two simulated examinations were created for 100 students by 100-item dichotomous examinations. Examination 2 contained 20 items common with those in examination 1. Examination 1 was systematically exposed to randomly missing student responses and to entire items being removed to determine the robustness of the RMM to missing data. The two examinations were then analyzed with the RMM individually and then in combination. Student scores and IRT measures were compared to determine if the IRT could successfully place the students from the two examinations on the same metric of measure.

RESULTS: The student measures were not affected when up to 20% of the student responses were randomly missing. Student measures continued to have high reliability and correlated with full matrix measures for up to 40% of items being dropped from the examination. Student scores and IRT measures correlated highly when the two examinations were combined.

CONCLUSIONS: The RMM can be successfully applied to small-sized class examinations, such as those at chiropractic, medical, and other health profession institutions. It is possible to place candidates from different administrations on the same metric of measure if there is as little as a 20% overlap of items between examinations. The RMM could assist faculty in determining if differences in candidate scores are caused by ability or item difficulty.

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