Compute Difficulty Level

The difficulty level of a question is the percentage of students in both the high-scoring (HS) group and low-scoring (LS) group who answer the question correctly (Worthen et al., 1999). In the previous example, 20 students were included in the analysis (10 HS and 10 LS), and  ten students (8 in HS and 2 in LS) answered the question correctly (option c).

Difficulty Level = (the number correct answers in both HS and LS / the total number of students in both groups) * 100

Difficulty Level = (10 / 20) * 100 = 50%

For norm referenced tests, the difficulty level should be between 20% to 80%. If it is around 20%, the question is ambiguous. If it is lower than 20%, the question may be too difficult or the response may be random. If it is around 25%, it is a good item but may be misspelled. If it is 95%, the question is too easy. The difficulty level of 50% is considered a good question.

Reference

• Worthen, B. R., White, K. R., Fan, X., & Sudweeks, R. R. (1999). Measurement and assessment in schools (2nd ed.). New York, NY: Addison Wesley Longman.