What is Similarity?
Turnitin does not check for plagiarism in a piece of work. Instead, we will check a student's work against our database, and if there are instances where a student's writing is similar to, or matches against, one of our sources, we will flag this for you to 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 of our database. If a student has used quotes and has referenced correctly, there will be instances where we will find a match. The similarity score simply highlights of any problem areas in a student's paper; you can then use this as an investigative tool, in order to determine if the match is or is not acceptable.
What's the difference between a match and a source?
Match - This is text that is very similar or the same as some text you have in your paper. Your matches are highlighted in Turnitin and the colors will correlate with the sources listed in your insight panel.
Source - The source is where a particular match has been found. This can be a web page, a student paper, or a published journal. Your sources are listed numerically in your insight panel and it is possible to have multiple matches for each source. Selecting one of your sources will reveal information like how many matches were found for that particular source and where each match was found on that web page, student paper, or journal.
Similarity Score Ranges
Similarity Reports provide a summary of matching or highly similar text found in a submitted paper. When a Similarity Report is available for viewing, a similarity score percentage will be made available. Similarity Reports that have not yet finished generating are represented by a grayed out icon in the Similarity column. Reports that are not available may not have generated yet, or assignment settings may be delaying the generation of the report.
Overwritten or resubmitted papers may not generate a new Similarity Report for a full 24 hours. This delay is automatic and allows resubmissions to correctly generate without matching to the previous draft.
The color of the report icon indicates the similarity score of the paper, based on the amount of matching or similar text that was uncovered. The percentage range is 0% to 100%. The possible 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
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.
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.
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.
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.
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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