The similarity score on a Turnitin report is nearly meaningless without interpretation. Both papers with (1) high and (2) low similarity scores still need further review.
(1) A high similarity score, on its own, offers no evidence of a failure that a student has failed to use sources properly. There are a number of reasons for what we might call false positives—passages highlighted by Turnitin that turn out to be properly cited:
- Turnitin sometimes flags titles that the student has listed in the text, footnotes, or bibliography. Titles are often long enough to produce a high similarity score.
- Turnitin sometimes flags text that the student has placed in quotation marks or in block quotations, even though the settings try to avoid these matches.
- Turnitin sometimes flags phrases that a discipline has established as technical names for key concepts, or language that everyone in the discipline uses to define a common idea. Such phrases are especially common in science and social science writing.
Here, for instance, are two passages Turnitin highlighted in sample papers but that would usually not be considered plagiarism: “the fear conditioning deficit model and the response modulation model” and “The inner boundary habitable zone is 0.335 AU, while the outer boundary habitable zone is 0.705 AU.”
- Disciplines have drastically different standards of how much similarity is acceptable.
Even a long passage with substantial similarity may be acceptable in some fields or in some genres, depending on how clearly the student credits the original source.
For these reasons, no conclusions can be drawn from the similarity score alone. Instructors must carefully review the actual matches flagged in a similarity report.
(2) Some low-percentage matches can still be substantial. For instance, a student paper could be organized around a source’s main argument, but without attribution, leaving the impression that the student writer came up with the idea.
Reviewing Similarity Reports
You can view the similarity reports on an individual paper through SpeedGrader on Canvas. For a step by step description of the process, including video illustration, please see the Help Guide.
When you first begin to use Turnitin, you may find yourself curious about every score above 0. As noted, many papers with low similarity scores will have no problems with correct attribution. As you review more similarity reports, you will develop a sense of which scores might indicate something interesting. This range will vary depending both on the academic discipline and on the specific assignment.
When you find similarities that are not the false positives described above, you can get advice on how to address different kinds of errors by consulting Categories of Source Misuse.
Even papers with similarity scores of 0 can have problems with source use. Such papers are less likely to be plagiarized. (Although there are some sources outside of Turnitin’s reach, these are dwindling as more texts come online.) But if the purpose of research is to help students enter a conversation with previous knowledge, then a perfectly cited paper can still be immature or underdeveloped. Students who are new to research writing often drop sources in without synthesis, commentary, or interpretation—substituting the sources’ ideas for their own. Turnitin can help you identify failures of attribution, but only a live instructor can guide students towards a more robust engagement with sources.