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Understanding the Similarity Report
A typical submission made to an assignment in Turnitin generates a Similarity Report. The similarity score is a percentage of a paper's content that matches to Turnitin's databases; it is not an assessment of whether the paper includes plagiarized material. Turnitin does not check for plagiarism in a piece of work. Instead, we will check a student's work against our databases, and if there are instances where a student's writing is similar to, or matches against, one of our sources, we will bring this to the instructor's attention for review.
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.
It is perfectly natural for an assignment to match against some content in our databases. See examples below.
Similarity scoring examples
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 5 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 managed to acquire a copy of another student's paper. They submit this paper to Turnitin on 15th October and receive a similarity score of 25%. The student who originally wrote the paper submits it to Turnitin a week later, receiving a 100% similarity score.
In this case, regenerating the Similarity Report of the student who plagiarized will immediately identify collusion allowing you to follow institutional regulation.
Example 5:
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.
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