Interpreting Similarity Reports


Turnitin produces an Similarity Report and a Similarity Index for each assignment submission.

  • An Similarity Report highlights the text in a document which matches sources elsewhere on the Internet such as websites and online journals, as well as other assignments submitted to Turnitin.
  • The Similarity Index within the report tells you how much of the submitted work has been identified by Turnitin as matching other sources. It is shown as a percentage from 0% to 100%.

Similarity Reports are useful tool to help staff investigate potential plagiarism and should be used by students to develop their understanding of academic writing.

Viewing and interpreting similarity reports

Similarity Reports require careful interpretation. A high Similarity Index doesn’t indicate plagiarism. Text matches can be caused by text that is correctly referenced or by common language of the discipline.

The UWL Blackboard Help for Students website explains how to view and interpret originality reports . It is aimed at both students and staff. In addition, this video highlights some of the functionality you can use to investigate matched text. The first minute of the video isn’t applicable to UWL but see Document Viewer (from 1’18”), Excluding Sources (1’46”) and Evaluating Sources (2’10”).

Supporting Your Students

Most students feel anxious about assessment and Turnitin introduces an additional concern – that a system, rather than a person, is going to judge their work. Student misconceptions about Turnitin are more likely to persist without support. For example, they may believe that there is an acceptable level of plagiarism, represented by a threshold percentage for the Similarity Index.

The university’s Turnitin Originality Reports Policy (PDF) requires that all students are taught about Turnitin as part of their course and that they are given an opportunity to review an Originality Report for a formative piece of work early in their course.

Students are likely to be less anxious and better able to benefit from using Turnitin if they understand its aims, what it can and cannot do and how their lecturers will use it. Students also need support to make sure they know what they can learn from using Turnitin and what strategies to use in order to do so.

Suggested approaches

  • Ensure your students are aware of the university’s Avoiding Plagiarism guidance and the Interpreting Similarity Reports guidance.
  • Discuss Turnitin with students in the context of understanding academic integrity and becoming a good academic writer.
  • Explain that Turnitin is just a tool that staff use to assist in the detection plagiarism. Staff, not the system, make judgements about whether or not a student has plagiarised.
  • Make sure students know how you use the results.
  • Never give students a threshold percentage index as it misrepresents what the index signifies.
  • Allow your students to see their originality reports and encourage them to look into all matches that are identified, whatever the overall index.
  • Encourage students to view the Turnitin report as feedback on their writing. Draw their attention to what the originality report can show them, such as poor paraphrasing or lack of quotation marks or citation.
  • If your class is too large for individual feedback on Turnitin reports, give generic feedback to the whole class, in conjunction with peer review and self-assessment activities.
  • Discuss Similarity Reports in your personal tutoring sessions on feedback.


Some of this advice is adapted from Supporting Your Students Use Turnitin, material produced by the E-Learning Unit at Queen Mary University of London. It is available for re-use under a creative commons BY-NC-SA licence. Under the terms of that licence the material here is also available for re-use.