What does a high discrimination index indicate about an exam item?

• A. It indicates the item is too easy
• B. It shows the item effectively differentiates high- from low-ability students
• C. It signals bias against some groups
• D. It suggests there are too many distractors

Answer: (B)

Discrimination index shows how well an item separates students by ability. When you compare the performance of higher- versus lower-ability students on a single item, a high discrimination index means the top group is much more likely to answer correctly than the bottom group. In other words, the item is tapping into true differences in knowledge or skill rather than luck or guesswork, making it a good indicator of what students truly understand.

That’s why the best choice is that the item effectively differentiates high- from low-ability students. A too-easy item often yields similar results across groups, giving low discrimination. Bias against some groups requires a different type of analysis (differential item functioning) beyond discrimination. And the number of distractors affects difficulty more than it does discrimination directly.