Which statistic is used to indicate the difficulty of a test?

Correct answer: Mean. The mean score (or the proportion of examinees answering correctly, which is the item difficulty index) shows how easy or hard a test was; a low mean indicates a difficult test.

• Standard deviation: Standard deviation shows the spread of scores, not difficulty.
• Correlation: Correlation shows the relationship between two variables.
• Item discrimination index: The item discrimination index shows how well an item separates high and low scorers, not how difficult it is.