The impact of 3-option responses to multiple-choice questions on guessing strategies and cut score determinations

Research has asserted MCQ items using three response options (one correct answer with two distractors) is comparable to, and possibly preferable over, traditional MCQ item formats consisting of four response options (e.g., one correct answer with three distractors), or five response options (e.g., one correct answer with four distractors). Some medical educators have also adopted the practice of using 3-option responses on MCQ exams as a response to the difficulty experienced in generating additional plausible distractors. To date, however, little work has explored how 3-option responses might impact validity threats stemming from random guessing strategies, and what impact 3-option responses might have on cut-score determinations, particularly in the context of medical education classroom assessments. The purpose of this work is to further explore these critically important considerations that largely have gone ignored in the medical education literature to this point.
A cumulative binomial distribution formula was used to calculate the probability that an examinee will answer at random a given number of items correctly on any exam (of any length). By way of a demonstration, a variety of scenarios were presented to illustrate how examination length and the number of response options impact examinees’ chances of passing a given examination, and how subsequent cut-score decisions may be impacted by these factors.
As a general rule, classroom assessments containing fewer items should utilize traditional 4-option or 5-option responses, whereas assessments of greater length are afforded greater flexibility in potentially utilizing 3-option responses.
More research on items with 3-option responses is needed to better understand what value, if any, 3-option responses truly add to classroom assessments, and in what contexts potential benefits might be discernible.