What Is Item Difficulty? The Quiz Quality Metric Most Teachers Ignore

Short answer. Item difficulty (denoted *p*) is the proportion of students who answered a given quiz question correctly. A question that 80% of students got right has *p* = 0.80. The metric is poorly named — *higher* difficulty value = *easier* question — but it's a foundational stat for evaluating quiz quality.

What the values mean

How to use it

For a typical quiz:

Item difficulty + item discrimination

Item difficulty alone is incomplete. A question with p = 0.50 might be:

Use both metrics together. A good quiz has medium-difficulty items with positive discrimination.

How modern quiz tools surface this

Most LMSs and quiz platforms show item difficulty after each quiz administration:

After every quiz, scan the difficulty distribution. The items with p > 0.95 (everyone right) and p < 0.15 (almost no one right) are usually the ones to review or rewrite.

Common mistakes

Item difficulty across high-stakes exams

For comparison, the average item difficulty on professional exams:

Classroom unit tests typically run easier (p around 0.75) because the goal is documenting that most students learned the material, not differentiating among them.

A diagnostic protocol after a quiz

After the first 10-20 students take a new quiz:

After 5-10 administrations, you have a refined item bank with known difficulty. AP/MCAT/NCLEX item banks went through this process for years before reaching production.

Why item difficulty matters less than discrimination

Two questions with the same difficulty (p = 0.60) can have very different value:

The first is a productive item; the second is a coin flip dressed up as a quiz question. Always check both metrics; never use difficulty alone.

Related reading

Generate a quiz and see per-question difficulty after the first 5 submissions.