A Benchmark for Overgeneration Detection in Biomedical Text Simplification

Berkay Chakar, Liana Ermakova, Jaap Kamps


Abstract
Large Language Models deployed for biomedical text simplification frequently produce overgeneration: extraneous content appended beyond the faithful simplification, including leaked model instructions, ungrounded medical claims, and repetitive text. Despite its prevalence, this failure mode remains largely unaddressed. We present a benchmark for document-level overgeneration detection, releasing two resources: SimpleOG-manual, 500 abstract-level examples with human-validated positive labels, and SimpleOG-auto, over 46,000 automatically labeled abstract-level examples derived from submissions to the CLEF 2025 SimpleText Track. Our method exploits the positional regularity of overgeneration in simplification output through sequence alignment, identifying trailing content that lacks a corresponding segment in the source. Human validation of 117 automatically flagged positives confirms ∼95% precision, with leaked model instructions accounting for 75.7% of confirmed cases. Analysis across teams and models reveals that overgeneration is primarily driven by system-level choices, such as prompting and post-processing, rather than by model architecture. We evaluate three detection paradigms and find that sentence similarity (F1 = 0.731, ROC-AUC = 0.915) surprisingly outperforms both NLI-based and LLM-based approaches, suggesting that overgenerated content occupies distinct semantic regions from source material.
Anthology ID:
2026.determit-1.2
Volume:
Proceedings of the 2nd Workshop on Evaluating Text Difficulty in a Multilingual Context (DeTermIt! 2026)
Month:
May
Year:
2026
Address:
Palma, Mallorca (Spain)
Editors:
Giorgio Maria Di Nunzio, Federica Vezzani, Liana Ermakova, Hosein Azarbonyad, Jaap Kamps
Venues:
DeTermIt | WS
SIG:
Publisher:
ELRA Language Resources Association (ELRA)
Note:
Pages:
12–21
Language:
External URL:
https://lrec.elra.info/lrec2026-ws-determit-02
DOI:
10.63317/3aodve3ow6a7
Bibkey:
Cite (ACL):
Berkay Chakar, Liana Ermakova, and Jaap Kamps. 2026. A Benchmark for Overgeneration Detection in Biomedical Text Simplification. In Proceedings of the 2nd Workshop on Evaluating Text Difficulty in a Multilingual Context (DeTermIt! 2026), pages 12–21, Palma, Mallorca (Spain). ELRA Language Resources Association (ELRA).
Cite (Informal):
A Benchmark for Overgeneration Detection in Biomedical Text Simplification (Chakar et al., DeTermIt 2026)
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