Evaluating Functional and Non-Functional Distractors and Their Relationship with Difficulty and Discrimination Indices in Four-Option Multiple-Choice Questions

Multiple-choice questions-one best answer (MCQ-OBA) is the most frequently accepted assessment tool in Iran’s medical universities. Writing functional distractors (FDs) is an important aspect of framing MCQ-OBA. This study aimed to assess FDs and non-functional distractors (NFDs) in MCQ-OBA and the association of distractor efficiency with difficulty and discrimination indices. This cross-sectional study was conducted at the Department of Immunology, the Ahvaz Jundishapur University of Medical Sciences. A total of 734 MCQ-OBA were reviewed, including 2,936 options (2,202 distractors and 734 correct responses). NFDs were defined as options chosen by <5% of examinees. Of the 734 MCQ-OBAs, 265 (36.1%) had 0 NFDs, 231 (31.5%) had 1 NFD, 146 (19.9%) had 2 NFDs, and 92 (12.5%) had 3 NFDs. The Pearson’s correlation showed a significant relationship between the difficulty index and the number of NFDs (r = 0.453; P < 0.0001). However, the correlation between the discrimination index and the number of NFDs was insignificant (r = 0.055; P = 0.135). The findings revealed that NFDs inversely affected the test quality of items. Items with more NFDs were easier and had poorer discriminatory power. The distractor function analysis and revision of NFDs serve as an important method to improve the quality of MCQ-OBA.