What Ensemble Brier Scores Hide: Evidence Routing at a Fixed Article-Exposure Budget in LLM Prediction-Market Forecasting

Avinash Goutham Aluguvelly


Abstract
We ask whether giving different evidence to different LLM forecasters creates useful diversity when the total article-exposure count is held fixed. Across 708 resolved prediction-market contracts, we compare six-member ensembles whose forecasters either share the same two article pair or are distributed evenly across three pairs, with both conditions using twelve article exposures. On 609 pre-market-end contracts, evidence routing reliably increases within-ensemble dispersion for GPT-4.1-mini, Qwen3-30B, and OLMo-3.1-32B. An exact Brier-score decomposition separates changes in member error, dispersion, and ensemble error, while a grouped-variance analysis attributes nearly all of the dispersion increase to differences between assigned article pairs rather than repeated sampling. Greater dispersion, however, does not automatically improve the en- semble: only Qwen’s reduction in ensemble Brier survives multiplicity correction, while GPT and OLMo show no statistically robust net improvement. Post-hoc controls show that more balanced routing further increases dispersion at a fixed evidence union, while an alterna- tive Qwen readout changes channel attribution without establishing a different net effect. Evidence routing therefore consistently increases forecast diversity in this setting, but its value depends on whether that diversity outweighs any loss in individual forecast quality.
Anthology ID:
2026.finnlp-1.30
Volume:
Proceedings of the 11th Workshop on Financial Technology and Natural Language Processing
Month:
October
Year:
2026
Address:
Budapest, Hungary
Editors:
Jimin Huang, Yongjae Lee, Sophia Ananiadou, Hsin-Hsi Chen, Hiroya Takamura, Chung-Chi Chen
Venues:
FinNLP | WS
SIG:
SIGFinTech
Publisher:
Association for Computational Linguistics
Note:
Pages:
373–382
Language:
URL:
https://aclanthology.org/2026.finnlp-1.30/
DOI:
Bibkey:
Cite (ACL):
Avinash Goutham Aluguvelly. 2026. What Ensemble Brier Scores Hide: Evidence Routing at a Fixed Article-Exposure Budget in LLM Prediction-Market Forecasting. In Proceedings of the 11th Workshop on Financial Technology and Natural Language Processing, pages 373–382, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
What Ensemble Brier Scores Hide: Evidence Routing at a Fixed Article-Exposure Budget in LLM Prediction-Market Forecasting (Aluguvelly, FinNLP 2026)
Copy Citation:
PDF:
https://aclanthology.org/2026.finnlp-1.30.pdf