Managing Overlapping Sources
Hi,
My institution uses the LTI 1.3 Turnitin integration with Canvas LMS. There is a behavior within the Enhanced Similarity Report that confuses me.
In one of my classes, there is a weekly reflection essay due that requires students to answer 2 questions. The second question is often the same from week to week so as to allow the student to improve their answer from week to week. However, if their answer the second question is good enough, they can just submit the same content for their answer to that question each week.
So, let's say a student does that, which means that about 150 words of their submission is exactly identical to at least one previous submission. What confuses me is that their previously submitted work does not automatically display a match in either the Match Groups or the Sources tabs. In order to display these significant matches, I have to click on Exclusions and then Include all Overlapping Sources. Why do I have to click through these menus to include such significant matches?
Thankfully, for this particular set of assignments, it's not a problem if the student reuses some of their previous work. However, there could be a situation where a student reusing previous work would qualify as plagiarism, and if the instructor/TA isn't aware of the matches hidden under Exclusions > Include all Overlapping Sources, this plagiarism could easily go undetected.
Thank you for your time,
Tim Baggenstos
3 replies
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Hey -
Thank you for taking the time to share this—and for explaining your use case so clearly. What you’re seeing is tied to how the Enhanced Similarity Report handles overlapping sources. By default, Turnitin may group or exclude certain matches (including a student’s own prior submissions) to reduce noise and avoid overinflating similarity scores—especially in cases where repeated or template-based content is expected.
That said, you’re absolutely right to call out the potential risk here. If significant matches (like reused prior work) are only visible after selecting Exclusions → Include all Overlapping Sources, there’s a real possibility that instructors or TAs could miss important signals—particularly in contexts where self-reuse would be considered plagiarism. Your example highlights that tension really well.
Because this behavior can depend on assignment settings, institutional repository configuration, and how overlapping matches are processed in the report, I’d recommend opening a support ticket so our technical team can:
- Confirm whether what you’re seeing is expected behavior in your specific setup
- Review your assignment and repository settings
- Share any available options to adjust how these matches are surfaced
You can submit a ticket through your Turnitin admin or via the support portal, and including a sample assignment or report (if possible) will help speed up the investigation.
Thanks again for raising this—it's a thoughtful and important question that gets at how we balance clarity with accuracy in similarity reporting.
- Audrey, The Turnitin Team