Question difficulty

Schreyer Institute
for Teaching Excellence
301 Rider Building
227 West Beaver Avenue
University Park, PA 16802
Phone: (814) 865-8681
Fax: (814) 865-8659

104-105 Pollock Building
University Park, PA 16802
Scanning: (814) 863-2802
Testing: (814) 863-8116
Fax: (814) 863-2322

A Division of Undergraduate Education at Penn State.

Question difficulty is defined as the proportion of students selecting the correct answer. The most effective questions in terms of distinguishing between high and low scoring students will be answered correctly by about half of the students. In practical terms, questions in most classroom tests will have a range of difficulties from low or easy (.90) to high or very difficult (.40). Questions having difficulty estimates outside of these ranges may not contribute much to the effective evaluation of student performance.

Very easy questions may not sufficiently challenge the most able students. However, having a few relatively easy questions in a test may be important to verify the mastery of some course objectives. Keep tests balanced in terms of question difficulty.
Very difficult questions, if they form most of a test, may produce frustration among students. Some very difficult questions are needed to challenge the best students.
Keeping records of question difficulty will enable you to select questions for a test so that the average difficulty is a certain value, say .80. The average difficulty of all the questions in a test multiplied by 100 will yield the average score in percentage terms that you could expect for a test created in this way.