RESUMO
How many incorrect response options (known as distractors) to use in multiple-choice questions has been the source of considerable debate in the assessment literature, especially relative to influence on the likelihood of students' guessing the correct answer. This study compared distractor use by second-year dental students in three successive oral and maxillofacial pathology classes that had three different examination question formats and scoring resulting in different levels of academic performance. One class was given all multiple-choice questions; the two other were given half multiple-choice questions, with and without formula scoring, and half un-cued short-answer questions. Use by at least 1 percent of the students was found to better identify functioning distractors than higher cutoffs. The average number of functioning distractors differed among the three classes and did not always correspond to differences in class scores. Increased numbers of functioning distractors were associated with higher question discrimination and greater question difficulty. Fewer functioning distractors fostered more effective student guessing and overestimation of academic achievement. Appropriate identification of functioning distractors is essential for improving examination quality and better estimating actual student knowledge through retrospective use of formula scoring, where the amount subtracted for incorrect answers is based on the harmonic mean number of functioning distractors.