The Difference Between AI Score and Plagiarism Score

When a Turnitin report comes back, it now shows two separate percentages. One is the similarity score, which most students already know. The other is the AI writing detection score, which was introduced in 2023. These two numbers measure completely different things, and confusing them leads students to make poor decisions about their work.
The similarity score measures how much of your text matches other published sources in Turnitin's database. This includes websites, academic journals, previously submitted student work, and other documents. A high similarity score suggests potential plagiarism or insufficient paraphrasing. Many universities allow similarity scores up to 15% or 20% before raising concerns, because some overlap is normal in academic writing.
The AI writing score measures something else entirely. It does not compare your text to any external source. It analyzes the statistical patterns in your writing to determine whether the text was likely generated by a large language model. A document can have a 0% similarity score and a 90% AI score. That means the text is entirely original in the sense that it does not match anything in the database, but it reads as AI generated based on how it is constructed.
This distinction matters because some students believe that paraphrasing AI output will resolve the problem. It addresses the similarity score. It does not address the AI score, because the issue is not the words themselves but the underlying patterns in how those words were arranged.
It also means a document can have a high similarity score while having a low AI score. That would indicate a human writer who relied heavily on direct quotation or failed to paraphrase sources properly.
Universities look at both numbers. Understanding what each one means helps you respond accurately if a tutor raises questions about your work.
Raphael can help you understand your Turnitin report and improve your writing accordingly. Reach him at +1(947)280-3413 or visit yourtutorraphael.com.

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