RESUMO
OBJECTIVES: The functionality of distracters in a multiple choice question plays a very important role. We examined the frequency and impact of functioning and non-functioning distracters on psychometric properties of 5-option items in clinical disciplines. METHODS: We analyzed item statistics of 1115 multiple choice questions from 15 summative assessments of undergraduate medical students and classified the items into five groups by their number of non-functioning distracters. We analyzed the effect of varying degree of non-functionality ranging from 0 to 4, on test reliability, difficulty index, discrimination index and point biserial correlation. RESULTS: The non-functionality of distracters inversely affected the test reliability and quality of items in a predictable manner. The non-functioning distracters made the items easier and lowered the discrimination index significantly. Three non-functional distracters in a 5-option MCQ significantly affected all psychometric properties (p < 0.5). The corrected point biserial correlation revealed that the items with 3 functional options were psychometrically as effective as 5-option items. CONCLUSIONS: Our study reveals that a multiple choice question with 3 functional options provides lower most limit of item format that has adequate psychometric property. The test containing items with less number of functioning options have significantly lower reliability. The distracter function analysis and revision of nonfunctioning distracters can serve as important methods to improve the psychometrics and reliability of assessment.
