Which statement best describes the difficult index?

• A. The item’s difficulty is determined by its length
• B. The difficult index measures how difficult a test item is
• C. It indicates how well an item discriminates
• D. It reflects the time required to answer the item

Answer: (B)

The difficult index describes how challenging a test item is by looking at the proportion of test-takers who answer it correctly. If many students get it right, the item is easy; if few do, the item is hard. It does not tell you about the item’s length, the time needed to answer, or how well the item differentiates between higher- and lower-scoring students (that last aspect is called discrimination). So the statement that the difficult index measures how difficult a test item is is the best description.