Understanding the Similarity Score

In this guide:

The Similarity Report

Turnitin does not check for plagiarism in writing. We do check all submissions against our database. If any text in a submission is similar to one of our sources, these matches are highlighted for you to review.

It is perfectly natural for a submission to match against some of our database. Our database includes billions of web pages: both current and archived content from the internet, a repository of works students have submitted to Turnitin in the past, and a collection of documents, which comprises thousands of periodicals, journals, and publications.

Even when a submission has quotation marks and references, the quoted text will show as a match. The similarity score is simply the percentage of text in a submission that matched to other sources. Use this as a tool within your review process to make your own determination if any academic misconduct is present.

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Similarity score percentage ranges

Turnitin Feedback Studio/Originality Check Turnitin Similarity/SimCheck

When a Similarity Report is available for viewing, a similarity score percentage displays in your assignment inbox.

The color of the report icon indicates the submission’s similarity score, based on the amount of matching text found. The percentage range is 0% to 100%. The colors for similarity ranges are:

  • Blue: No matching text
  • Green: One word to 24% matching text
  • Yellow: 25-49% matching text
  • Orange: 50-74% matching text
  • Red: 75-100% matching text

Scoring scenarios

Example 1:
A student may have submitted a paper to Turnitin in the past. If they had their name on that submission, it is entirely possible that, if you have not excluded small matches, their name is highlighted in their Similarity Report.

An instructor can rectify this issue by excluding by word number. In most cases, excluding 10 words should safely exclude a student's name from being highlighted in their Similarity Report.

Example 2:
A student may have used Turnitin to submit drafts of the same paper, meaning their final draft has resulted in a score of 100%.

As the instructor is likely aware that their student has submitted multiple times, they can rectify this issue by excluding the student's previous submissions from the Similarity Report.

Example 3:
A student has copied and pasted a chunk of text into their paper, due to a lack of knowledge on the topic they are covering. Their similarity score is 20%. In comparison, another student who has a firm basis of knowledge for the same assignment and knows enough to gather information from several sources to quote and reference correctly has a similarity score of 22%. Both students will be shown to have matches against our database. However, one of these students copied directly from a website, whereas the other provided properly sourced quotes.

Instructors can opt to exclude quotes from the Similarity Report to lower similarity scores where applicable.

Example 4:
A student has submitted a qualitative study to Turnitin, including a significant number of quotes and an extensive bibliography, as required for the topic of the paper. The student's similarity score is 53%; this exceeds the acceptable score set by their institution.

This issue could have been avoided if quotes and bibliography had been excluded from the Similarity Report.

How does Turnitin detect student collusion?

Collusion is typically identified when a student's work matches with another student's submission on the same assignment or to previous submissions. Consider the following scenario:

Eric acquired a copy of his classmate Jane's paper. Eric submits Jane's paper as his own and receives a similarity score of 25%. Jane, who originally wrote the paper, submits her work a few days later and receives a 100% similarity score. Turnitin can identify that collusion has taken place in this scenario by running a final similarity check against all submitted assignments after the due date, thereby ensuring that every student is subject to the same level of scrutiny, regardless of when they submitted their assignments.

To enable collusion checking, papers must be set to be added to the standard paper repository or your institution’s paper repository, and Similarity Reports must be set to generate “immediately (can overwrite reports until due date)” or “on the due date."

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