Optimal discrimination index and discrimination efficiency for essay questions
1Office of Educational Services, Faculty of Medicine, The Chinese University of Hong Kong, Shatin, Hong Kong, chan50b@gmail.com.
Journal of Applied Measurement
|February 13, 2014
Summary
Discrimination index guidelines for essay questions differ from multiple-choice tests. Optimal values for essay questions, particularly with a 50% passing mark, range from 0.12 to 0.31, not 0.40 or higher.
Area of Science:
- Educational Measurement
- Psychometrics
Background:
- Standard guidelines for discrimination index are often applied to both multiple-choice and essay questions.
- This indiscriminate application may not be appropriate due to the inherent differences in question formats.
Purpose of the Study:
- To independently derive the optimal discrimination index for essay questions.
- To establish appropriate guidelines for the discrimination index of essay questions.
Main Methods:
- Derived the optimal discrimination index for essay questions under normality conditions.
- Analyzed the satisfactory region for the discrimination index with a 50% passing mark.
- Investigated the relationship between the optimal discrimination index and the range of scores.
- Defined discrimination efficiency.
Main Results:
- The satisfactory region for the discrimination index of essay questions (50% passing mark) is 0.12–0.31.
- Optimal discrimination index for essay questions increases proportionally with the score range.
- Discrimination efficiency was defined as the ratio of observed to optimal discrimination index.
Conclusions:
- Recommended guidelines for the discrimination index of essay questions are provided.
- The study highlights the need for distinct criteria for evaluating essay question quality compared to multiple-choice questions.
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