VII. Key Components of Item Analysis
b. Discrimination Index: Identifying high-quality test items
The discrimination index is a metric used in item analysis to determine the quality of assessment questions. It measures how well a question can differentiate between high-performing and low-performing students. A positive discrimination index indicates that the question effectively distinguishes strong students from weaker ones, while a negative value suggests that low-performing students performed better than high-performing students on that question.
BASIC Information
READ
Evaluation Of Discrimination Index Of Single Best Response Type Of Multiple Choice Questions In Physiology By Item Analysis.INTERMEDIATE Information
READ
Correlation between difficulty & discrimination indices of MCQs in formative exam in PhysiologyADVANCED Information
Calculation:
Subtract the proportion of low-performing students who answered correctly from the proportion of high-performing students who answered correctly.
Positive value: Indicates strong discrimination and effective differentiation.
Negative value: Indicates weak or reversed discrimination.
READ
Do Item-discrimination Indices Really Help Us to Improve Our Tests?Positive Discrimination Index:
Indicates that the question effectively distinguishes between strong and weak students.
Suggests that the question contributes meaningfully to the assessment's quality.
Negative Discrimination Index:
Suggests that the question is flawed or poorly worded.
Students who perform poorly overall answered it correctly, while strong students did not.
READ
To What Extent Are Item Discrimination Values Realistic? A New Index for Two-Dimensional StructuresContextual Interpretation:
Consider the subject matter and learning objectives when interpreting the discrimination index.
A positive discrimination index is valuable when it aligns with the expected performance.
PA Program:
Question: "Which diagnostic test should be ordered first for a patient with suspected pneumonia?"
Calculation: Positive discrimination index.
Interpretation: The question effectively distinguishes students who understand diagnostic priority.
In Summary: The discrimination index in item analysis assesses the ability of an assessment question to differentiate between high-performing and low-performing students. A positive discrimination index indicates effective question quality, while a negative index suggests a need for question revision. Advanced teachers contextualize the interpretation of the discrimination index, considering subject matter and learning objectives to determine its value in assessing student performance.