Discrimination index interpretation: A high positive discrimination index indicates

• A. The item differentiates weakly between groups
• B. The item is too easy
• C. The item is too hard
• D. The item differentiates well between high- and low-performing students

Answer: (D)

Discrimination index tells you how well an item separates students by ability. It compares how the top-performing group and the bottom-performing group answer the item. A high positive value means the top group is much more likely to answer correctly than the bottom group, so the item is doing a good job distinguishing those who have mastered the material from those who have not. For example, if 85% of the high-ability group gets it right but only 25% of the lower-ability group does, the item shows strong discrimination. If an item is too easy or too hard, both groups tend to perform similarly, leading to a small discrimination value. A negative discrimination would indicate the lower group does better, which signals a problem with the item. Therefore, a high positive discrimination index indicates the item differentiates well between high- and low-performing students.