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Comment by vondur | Hacker News Reader

I agree. Most campuses use a product called Turnitin, which was originally designed to check for plagiarism. Now they claim it can detect AI-generated content with about 80% accuracy, but I don’t think anyone here believes that.

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I had Turn It In mark my work as plagiarism some years ago and I had to fight for it. It was clear the teacher wasn’t doing their job and blindly following the tool.

What happened is that I did a Q&A worksheet but in each section of my report I reiterated the question in italics before answering it.

The reiterated questions of course came up as 100% plagiarism because they were just copied from the worksheet.

This matches my experience pretty well. My high school was using it 15 years ago and it was a spotty, inconsistent morass even back then. Our papers were turned in over the course of the semester, and late into the year you’d get flagged for “plagiarizing” your own earlier paper.

> you’d get flagged for “plagiarizing” your own earlier paper

Wow I'd have been screwed, so many of my high school papers were just rewrites and improvements on stuff I wrote in earlier years.

Funny how it's the teachers that are plagiarizing the work of the tools.

80% is catastrophic though. In a classroom of 30 all honest pupils, 6 will get a 0 mark because the software says its AI?

80% accuracy could mean 0 false negatives and 20% false positives.

My point is that accuracy is a terrible metric here and sensitivity, specificity tell us much more relevant information to the task at hand. In that formulation, a specificity < 1 is going to have false positives and it isn't fair to those students to have to prove their innocence.

That's more like the false positive rate and false negative rate.

If we're being literal, accuracy is (number correct guesses) / (total number of guesses). Maybe the folks at turnitin don't actually mean 'accuracy', but if they're selling an AI/ML product they should at least know their metrics.

It depends on their test dataset. If the test set was written 80% by AI and 20% by humans, a tool that labels every essay as AI-written would have a reported accuracy of 80%. That's why other metrics such as specificity and sensitivity (among many others) are commonly reported as well.

Just speaking in general here -- I don't know what specific phrasing TurnItIn uses.

The promise (not saying that it works) is probably that 20% of people who cheated will not get caught. Not that 20% of the work marked as AI is actually written by humans.

I suppose 80% means you don't give them a 0 mark because the software says it's AI, you only do so if you have other evidence reinforcing the possibility.

no, you multiply their result by .8 to account for the "uncertainty"! /s

I think it means every time AI is used, it will detect it 80% of the time. Not that 20% of the class will marked as using AI.

you're missing out on the false positives though; catching 80% of cheaters might be acceptable but 20% false positives (not the same thing as 20% of the class) would not be acceptable. AI generated content and plagarism are completely different detection problems.

For sure.

False positives with technology that is non-deterministic is guaranteed.

It's more than slightly comedic people being amazed when LLM math works as it's created to.

> but I don’t think anyone here believes that.

All it takes is one moron with power and a poor understanding of statistics.

Had a professor use this but it was student-led. We had to run it through ourselves and change our stuff enough to get a high enough mark to pass TurnItIn. Avoided the false allegations problems at least.

If they are serious they should realize that "80% accuracy" is almost meaningless for this kind of classifier. They should publish a confusion matrix if they haven't already.

I have had Turnitin flag my work as plagiarism for quotes from the relevant text that were quite clearly indicated as quotes.

It's shit software for schools and teachers to cover their ass. Nothing more, and deserves no more attention.

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