Origin bias of test items compromises the validity and fairness of curriculum comparisons.

Objective To determine whether items of progress tests used for inter-curriculum comparison favour students from the medical school where the items were produced (i.e. whether the origin bias of test items is a potential confounder in comparisons between curricula). Methods We investigated scores of students from different schools on subtests consisting of progress test items constructed by authors from the different schools. In a cross-institutional collaboration between 3 medical schools, progress tests are jointly constructed and simultaneously administered to all students at the 3 schools. Test score data for 6 consecutive progress tests were investigated. Participants consisted of approximately 5000 undergraduate medical students from 3 medical schools. The main outcome measure was the difference between the scores on subtests of items constructed by authors from 2 of the collaborating schools (subtest difference score). Results The subtest difference scores showed that students obtained better results on items produced at their own schools. This effect was more pronounced in Years 2–5 of the curriculum than in Year 1, and diminished in Year 6. Conclusions Progress test items were subject to origin bias. As a consequence, all participating schools should contribute equal numbers of test items if tests are to be used for valid and fair inter-curriculum comparisons. [ABSTRACT FROM AUTHOR]