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An investigation into the optimal number of distractors in single-best answer exams.

ABSTRACT: In UK medical schools, five-option single-best answer (SBA) questions are the most widely accepted format of summative knowledge assessment. However, writing SBA questions with four effective incorrect options is difficult and time consuming, and consequently, many SBAs contain a high frequency of implausible distractors. Previous research has suggested that fewer than five-options could hence be used for assessment, without deterioration in quality. Despite an existing body of empirical research in this area however, evidence from undergraduate medical education is sparse. The study investigated the frequency of non-functioning distractors in a sample of 480 summative SBA questions at Cardiff University. Distractor functionality was analysed, and then various question models were tested to investigate the impact of reducing the number of distractors per question on examination difficulty, reliability, discrimination and pass rates. A survey questionnaire was additionally administered to 108 students (33 % response rate) to gain insight into their perceptions of these models. The simulation of various exam models revealed that, for four and three-option SBA models, pass rates, reliability, and mean item discrimination remained relatively constant. The average percentage mark however consistently increased by 1-3 % with the four and three-option models, respectively. The questionnaire survey revealed that the student body had mixed views towards the proposed format change. This study is one of the first to comprehensively investigate distractor performance in SBA examinations in undergraduate medical education. It provides evidence to suggest that using three-option SBA questions would maximise efficiency whilst maintaining, or possibly improving, psychometric quality, through allowing a greater number of questions per exam paper.

SUBMITTER: Kilgour JM

PROVIDER: S-EPMC4923093 | biostudies-literature | 2016 Aug

REPOSITORIES: biostudies-literature

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An investigation into the optimal number of distractors in single-best answer exams.

Kilgour James M JM Tayyaba Saadia S

Advances in health sciences education : theory and practice 20151123 3

In UK medical schools, five-option single-best answer (SBA) questions are the most widely accepted format of summative knowledge assessment. However, writing SBA questions with four effective incorrect options is difficult and time consuming, and consequently, many SBAs contain a high frequency of implausible distractors. Previous research has suggested that fewer than five-options could hence be used for assessment, without deterioration in quality. Despite an existing body of empirical researc ...[more]

PMID: 26597452

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Project description:OBJECTIVES:The study aimed to compare candidate performance between traditional best-of-five single-best-answer (SBA) questions and very-short-answer (VSA) questions, in which candidates must generate their own answers of between one and five words. The primary objective was to determine if the mean positive cue rate for SBAs exceeded the null hypothesis guessing rate of 20%. DESIGN:This was a cross-sectional study undertaken in 2018. SETTING:20 medical schools in the UK. PARTICIPANTS:1417 volunteer medical students preparing for their final undergraduate medicine examinations (total eligible population across all UK medical schools approximately 7500). INTERVENTIONS:Students completed a 50-question VSA test, followed immediately by the same test in SBA format, using a novel digital exam delivery platform which also facilitated rapid marking of VSAs. MAIN OUTCOME MEASURES:The main outcome measure was the mean positive cue rate across SBAs: the percentage of students getting the SBA format of the question correct after getting the VSA format incorrect. Internal consistency, item discrimination and the pass rate using Cohen standard setting for VSAs and SBAs were also evaluated, and a cost analysis in terms of marking the VSA was performed. RESULTS:The study was completed by 1417 students. Mean student scores were 21 percentage points higher for SBAs. The mean positive cue rate was 42.7% (95% CI 36.8% to 48.6%), one-sample t-test against ≤20%: t=7.53, p<0.001. Internal consistency was higher for VSAs than SBAs and the median item discrimination equivalent. The estimated marking cost was £2655 ($3500), with 24.5 hours of clinician time required (1.25 s per student per question). CONCLUSIONS:SBA questions can give a false impression of students' competence. VSAs appear to have greater authenticity and can provide useful information regarding students' cognitive errors, helping to improve learning as well as assessment. Electronic delivery and marking of VSAs is feasible and cost-effective.

Project description:During the preclinical years, single-best-answer multiple-choice questions (SBA-MCQs) are often used to test the higher-order cognitive processes of medical students (such as application and analysis) while simultaneously assessing lower-order processes (like knowledge and comprehension). Consequently, it can be difficult to pinpoint which learning outcome has been achieved or needs improvement. We developed a new scoring system for SBA-MCQs using a step-by-step methodology to evaluate each learning outcome independently. Enrolled in this study were third-year medical students (n = 316) who had registered in the basic microbiology course at the Faculty of Medicine, Siriraj Hospital, Mahidol University during the academic year 2017. A step-by-step SBA-MCQ with a new scoring system was created and used as a tool to evaluate the validity of the traditional SBA-MCQs that assess two separate outcomes simultaneously. The scores for the two methods, in percentages, were compared using two different questions (SBA-MCQ1 and SBA-MCQ2). SBA-MCQ1 tested the students' knowledge of the causative agent of a specific infectious disease and the basic characteristics of the microorganism, while SBA-MCQ2 tested their knowledge of the causative agent of a specific infectious disease and the pathogenic mechanism of the microorganism. The mean score obtained with the traditional SBA-MCQs was significantly lower than that obtained with the step-by-step SBA-MCQs (85.9% for the traditional approach versus 90.9% for step-by-step SBA-MCQ1; p < 0.001; and 81.5% for the traditional system versus 87.4% for step-by-step SBA-MCQ2; p < 0.001). Moreover, 65.8% and 87.8% of the students scored lower with the traditional SBA-MCQ1 and the traditional SBA-MCQ2, respectively, than with the corresponding sets of step-by-step SBA-MCQ questions. These results suggest that traditional SBA-MCQ scores need to be interpreted with caution because they have the potential to underestimate the learning achievement of students. Therefore, the step-by-step SBA-MCQ is preferable to the traditional SBA-MCQs and is recommended for use in examinations during the preclinical years.

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An investigation into the optimal number of distractors in single-best answer exams.

Publications

An investigation into the optimal number of distractors in single-best answer exams.

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