Synthetic Data Can Mislead Evaluations: Membership Inference as Machine Text Detection

Fuente: arXiv
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Main Authors: Naseh, Ali, Mireshghallah, Niloofar
Format: Preprint
Published: 2025
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author Naseh, Ali
Mireshghallah, Niloofar
author_facet Naseh, Ali
Mireshghallah, Niloofar
contents Recent work shows membership inference attacks (MIAs) on large language models (LLMs) produce inconclusive results, partly due to difficulties in creating non-member datasets without temporal shifts. While researchers have turned to synthetic data as an alternative, we show this approach can be fundamentally misleading. Our experiments indicate that MIAs function as machine-generated text detectors, incorrectly identifying synthetic data as training samples regardless of the data source. This behavior persists across different model architectures and sizes, from open-source models to commercial ones such as GPT-3.5. Even synthetic text generated by different, potentially larger models is classified as training data by the target model. Our findings highlight a serious concern: using synthetic data in membership evaluations may lead to false conclusions about model memorization and data leakage. We caution that this issue could affect other evaluations using model signals such as loss where synthetic or machine-generated translated data substitutes for real-world samples.
format Preprint
id arxiv_https___arxiv_org_abs_2501_11786
institution arXiv
publishDate 2025
record_format arxiv
spellingShingle Synthetic Data Can Mislead Evaluations: Membership Inference as Machine Text Detection
Naseh, Ali
Mireshghallah, Niloofar
Computation and Language
Cryptography and Security
Machine Learning
Recent work shows membership inference attacks (MIAs) on large language models (LLMs) produce inconclusive results, partly due to difficulties in creating non-member datasets without temporal shifts. While researchers have turned to synthetic data as an alternative, we show this approach can be fundamentally misleading. Our experiments indicate that MIAs function as machine-generated text detectors, incorrectly identifying synthetic data as training samples regardless of the data source. This behavior persists across different model architectures and sizes, from open-source models to commercial ones such as GPT-3.5. Even synthetic text generated by different, potentially larger models is classified as training data by the target model. Our findings highlight a serious concern: using synthetic data in membership evaluations may lead to false conclusions about model memorization and data leakage. We caution that this issue could affect other evaluations using model signals such as loss where synthetic or machine-generated translated data substitutes for real-world samples.
title Synthetic Data Can Mislead Evaluations: Membership Inference as Machine Text Detection
topic Computation and Language
Cryptography and Security
Machine Learning
url https://arxiv.org/abs/2501.11786