@inproceedings{chae-etal-2026-self,
title = "Self- and Other-Labels Induce Bidirectional Bias in {LLM} Judges",
author = "Chae, Songeun and
Kim, Min and
Jung, Donghoon and
Choi, Seojin and
Jung, Seohyon",
editor = "Lee, Hung-Yi and
Dev, Sunipa and
Li, Jessy and
Elliott, Desmond",
booktitle = "Findings of the {A}ssociation for {C}omputational {L}inguistics: {EMNLP} 2026",
month = oct,
year = "2026",
address = "Budapest, Hungary",
publisher = "Association for Computational Linguistics",
url = "https://aclanthology.org/2026.findings-emnlp.1571/",
doi = "10.18653/2026.findings-emnlp.1571",
pages = "33466--33482",
ISBN = "979-8-89176-462-0",
abstract = "As LLM-as-a-judge becomes increasingly widespread, self-preference{---}the tendency of a judge to favor its own outputs{---}raises growing concerns about evaluation reliability. However, this bias has been studied predominantly on generated text, where stylistic features and response quality are inevitably conflated. As a result, existing measurements cannot separate genuine self-preference from these confounds. We address this limitation by changing the object of evaluation: instead of judging generated text, ten LLMs assess sets of narrative constraints selected from a shared pool, which carry no stylistic fingerprint yet retain a recoverable model-specific signature. Two experiments on this task yield complementary findings. Under blind evaluation, self-preference disappears, with a small effect remaining in the opposite direction once selection quality and judge severity are controlled. Under matched quality, however, self- and other-labels alone{---}without naming any model{---}shift scores bidirectionally. LLM judges inflate scores for self-labeled selections and deflate those for other-labeled ones regardless of the selection{'}s actual source. We make two contributions: 1) authorship attribution is a distinct driver of evaluation bias, and 2) ground-truth-free tasks can serve as controlled instruments for studying LLM judge behavior."
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<abstract>As LLM-as-a-judge becomes increasingly widespread, self-preference—the tendency of a judge to favor its own outputs—raises growing concerns about evaluation reliability. However, this bias has been studied predominantly on generated text, where stylistic features and response quality are inevitably conflated. As a result, existing measurements cannot separate genuine self-preference from these confounds. We address this limitation by changing the object of evaluation: instead of judging generated text, ten LLMs assess sets of narrative constraints selected from a shared pool, which carry no stylistic fingerprint yet retain a recoverable model-specific signature. Two experiments on this task yield complementary findings. Under blind evaluation, self-preference disappears, with a small effect remaining in the opposite direction once selection quality and judge severity are controlled. Under matched quality, however, self- and other-labels alone—without naming any model—shift scores bidirectionally. LLM judges inflate scores for self-labeled selections and deflate those for other-labeled ones regardless of the selection’s actual source. We make two contributions: 1) authorship attribution is a distinct driver of evaluation bias, and 2) ground-truth-free tasks can serve as controlled instruments for studying LLM judge behavior.</abstract>
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%0 Conference Proceedings
%T Self- and Other-Labels Induce Bidirectional Bias in LLM Judges
%A Chae, Songeun
%A Kim, Min
%A Jung, Donghoon
%A Choi, Seojin
%A Jung, Seohyon
%Y Lee, Hung-Yi
%Y Dev, Sunipa
%Y Li, Jessy
%Y Elliott, Desmond
%S Findings of the Association for Computational Linguistics: EMNLP 2026
%D 2026
%8 October
%I Association for Computational Linguistics
%C Budapest, Hungary
%@ 979-8-89176-462-0
%F chae-etal-2026-self
%X As LLM-as-a-judge becomes increasingly widespread, self-preference—the tendency of a judge to favor its own outputs—raises growing concerns about evaluation reliability. However, this bias has been studied predominantly on generated text, where stylistic features and response quality are inevitably conflated. As a result, existing measurements cannot separate genuine self-preference from these confounds. We address this limitation by changing the object of evaluation: instead of judging generated text, ten LLMs assess sets of narrative constraints selected from a shared pool, which carry no stylistic fingerprint yet retain a recoverable model-specific signature. Two experiments on this task yield complementary findings. Under blind evaluation, self-preference disappears, with a small effect remaining in the opposite direction once selection quality and judge severity are controlled. Under matched quality, however, self- and other-labels alone—without naming any model—shift scores bidirectionally. LLM judges inflate scores for self-labeled selections and deflate those for other-labeled ones regardless of the selection’s actual source. We make two contributions: 1) authorship attribution is a distinct driver of evaluation bias, and 2) ground-truth-free tasks can serve as controlled instruments for studying LLM judge behavior.
%R 10.18653/2026.findings-emnlp.1571
%U https://aclanthology.org/2026.findings-emnlp.1571/
%U https://doi.org/10.18653/2026.findings-emnlp.1571
%P 33466-33482
Markdown (Informal)
[Self- and Other-Labels Induce Bidirectional Bias in LLM Judges](https://aclanthology.org/2026.findings-emnlp.1571/) (Chae et al., Findings 2026)
ACL