FairSynth: Instrument-Relative Evaluation and Calibration of LLM Survey Simulations for Measurement Fairness

Guangrui Fan, DanDan Liu, Qian Guo, Xueying Niu, Lihu Pan


Abstract
Large language models (LLMs) are increasingly used as virtual survey respondents, yet most evaluations compare only item-level marginal response distributions. Such evaluations can miss two failures central to computational social science: synthetic respondents may distort correlations among attitudes, and errors may be distributed unevenly across countries or demographic groups. We introduce FairSynth, an instrument-relative framework for auditing and calibrating closed-ended, answer-only LLM survey simulations against existing anchor surveys. FairSynth evaluates marginal fidelity, Structural Attitude Fidelity (item–item correlation similarity), group representation error, distributional flattening, and between-group sign reversals. It then applies a model-agnostic post-hoc logit-shift layer with shared group parameters to reduce disparities in representation error while preserving attitude structure. Experiments on World Values Survey Wave 7 and General Social Survey 2022 show that FairSynth reduces worst-group representation error and sign reversals while improving structural fidelity on the evaluated questionnaires. FairSynth is not a substitute for human surveys; it is a measurement-fairness toolkit for auditing, stress-testing, and calibrating synthetic survey simulations when anchor data are available.
Anthology ID:
2026.findings-emnlp.714
Volume:
Findings of the Association for Computational Linguistics: EMNLP 2026
Month:
October
Year:
2026
Address:
Budapest, Hungary
Editors:
Hung-Yi Lee, Sunipa Dev, Jessy Li, Desmond Elliott
Venue:
Findings
SIG:
SIGDAT
Publisher:
Association for Computational Linguistics
Note:
Pages:
14992–15012
Language:
URL:
https://aclanthology.org/2026.findings-emnlp.714/
DOI:
10.18653/2026.findings-emnlp.714
Bibkey:
Cite (ACL):
Guangrui Fan, DanDan Liu, Qian Guo, Xueying Niu, and Lihu Pan. 2026. FairSynth: Instrument-Relative Evaluation and Calibration of LLM Survey Simulations for Measurement Fairness. In Findings of the Association for Computational Linguistics: EMNLP 2026, pages 14992–15012, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
FairSynth: Instrument-Relative Evaluation and Calibration of LLM Survey Simulations for Measurement Fairness (Fan et al., Findings 2026)
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PDF:
https://aclanthology.org/2026.findings-emnlp.714.pdf