Predictability of Discrimination Coefficient and Difficulty Index of Psychiatry Multiple-Choice Questions

Background: Multiple-choice questions are among the most common written tests. This study aimed to evaluate the faculty members’ability to determine and predict the level of difficulty and discrimination coefficient of multiple-choice tests at Psychiatry Department. Methods: All faculty members at Psychiatry Department of Iran University of Medical Sciences participated in this study. The difficulty and discrimination coefficient of all questions (150 questions) of the mid-term exam of psychiatric residents were measured with both software program and formulas by hand. Then, from each group of questions with high, medium, and low difficulty coefficient, 10 questions (30 questions in total) were selected and provided to faculty members for ranking each question in terms of difficulty and discrimination coefficient. Finally, the correlation between faculty members’ evaluation and standard results was measured by the Spearman’s correlation. To calculate the discrimination coefficient, the number of people who answered a question correctly in the low-score group was subtracted from the high-score group and then the result was divided by the number of people in a group. Results: Twenty-five faculty members participated in this study. There was a significant negative correlation between difficulty level and discrimination coefficient in the whole group (r=-0.196, p=0.045), but this was not the case in the upper and lower groups (r=-0.063, p=0.733). In addition, the correlation between the discrimination coefficient obtained from the formula and the average discrimination coefficient of faculty members was not significant (r=-0.047, p=0.803). Conclusion: It seems that the ability of faculty members to predict the discrimination coefficient and difficulty level of questions is not sufficient.