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Use your Canvas quiz discrimination index to fix weak questions

Canvas reports how well each question separates high scorers from low scorers. Here is how to read that number and rewrite the questions that fall short.

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How to read a discrimination index in Canvas

Your Canvas quiz discrimination index shows whether a question separates students who understood the material from those who did not. It is based on how the top and bottom scoring groups answered each item, and the value runs from -1 to 1.

Check the number of responses, since very small classes produce unstable values that need careful reading.
Compare the discrimination index with the item's difficulty before deciding to drop a question.
Look at which wrong options students chose most often to find distractors that mislead.
Re-test revised items on a later quiz rather than judging them on a single attempt.

Example discrimination index questions for item analysis

What does a discrimination index of 0.45 indicate?A strong item: high scorers answered it correctly far more often than low scorers, so it separates understanding well.

What might a discrimination index of -0.10 signal?A possible problem: low scorers outperformed high scorers on this item, so check the answer key and wording for errors.

Which students does the classic discrimination index compare?The top and bottom scoring groups, often the highest and lowest 27 percent of students, on the item in question.

What range do discrimination index values fall within?From -1 to +1. Values near +1 mean the item separates high and low scorers strongly, and values near 0 mean it does not.

Why check difficulty alongside discrimination?A very easy or very hard item can have a low discrimination value even when well written, so both numbers guide revision decisions.

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How it works

Run the quiz in Canvas

Publish the quiz and let students finish so Canvas has enough responses to calculate item statistics.

Open item analysis

In the quiz statistics, check the discrimination index for each question. Values near 0.3 or higher usually separate strong and weak performers well.

Rewrite the weak items

Revise or replace questions with low or negative values, then generate fresh versions from your notes with DeckOwl.

Values around 0.3 and above generally mean the question discriminates well. Values between about 0.2 and 0.3 are worth a second look, and anything near zero or negative suggests the question may be confusing, miskeyed, or testing something other than the topic.

DeckOwl does not calculate this number, but it can help you write replacement questions with explanations drawn from the same notes, so the revised item tests the same idea more clearly.

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Frequently asked questions

What is a good discrimination index for a quiz question?

Many instructors treat values of 0.3 or higher as strong, 0.2 to 0.29 as acceptable, and anything below 0.2 as a question to review. Compare values across the whole quiz, since context matters.

Why would a question have a negative discrimination index?

Students who scored low overall answered it correctly more often than high scorers did. That usually points to an incorrect answer key, ambiguous wording, or a question that rewards a common misconception.

Does DeckOwl calculate the discrimination index in Canvas?

No. Canvas calculates item statistics after students answer, while DeckOwl generates questions with explanations from your own material. PDF and DOCX exports are on Plus, and QTI 2.1 and Moodle XML export are on Pro.

Can I import DeckOwl quizzes into Canvas?

Pro includes QTI 2.1 export, so check that your Canvas setup accepts that format before importing. Free accounts can study generated questions in the browser without exports.

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