Abstract
Introduction: The number of distractors needed for high quality multiple choice questions (MCQs) will be determined by many factors. These include firstly whether English language is their mother tongue or a foreign language; secondly whether the instructors who construct the questions are experts or not; thirdly the time spent on constructing the options is also an important factor. It has been observed by Tarrant et al that more time is often spent on constructing questions than on tailoring sound, reliable, and valid distractors.
Objectives: Firstly, to investigate the effects of reducing the number of options on psychometric properties of the item. Secondly, to determine the frequency of functioning distractors among three or four options in the MCQs examination of the dermatology course in University of Bahri, College of Medicine.
Materials and methods: This is an experimental study which was performed by means of a dermatology exam, MCQs type. Forty MCQs, with one correct answer for each question were constructed. Two sets of this exam paper were prepared: in the first one, four options were given, including one key answer and three distractors. In the second set, one of the three distractors was deleted randomly, and the sequence of the questions was kept in the same order. Any distracter chosen by less than 5% of the students was regarded as non-functioning. Kuder-Richardson Formula 20 (Kr-20) measures the internal consistency and reliability of an examination with an acceptable range 0.8-1.0. Chi square test was used to compare the distractors in the two exams.
Results: A significant difference was observed in discrimination and difficulty indexes for both sets of MCQs. More distractors were non-functional for set one (of four options), but slightly more reliable. The reliability (Kr-20) was slightly higher for set one (of four options). The average marks in option three and four were 34.163 and 33.140, respectively.
Conclusion: Compared to set 1 (four options), set 2 (of three options) was more discriminating and associated with low difficulty index but its reliability was low.