arXiv Computation and Language

What Pairwise Evaluation Misses: Reward Scores across Prompts

The paper investigates how reward models, used for preference optimization and ranking, can be biased by prompt-specific effects that are not captured by pairwise evaluation. By comparing between‑prompt variance in model scores to human ratings, the authors find that reward scores cluster strongly by prompt, often more so than human judgments. They propose a human‑referenced audit that examines between‑prompt variation, sensitivity to incorrect prompts, and usefulness for response selection, and demonstrate that adjusting for prompt means can reduce misleading global selection of responses.

arXiv Computation and Language
3d ago

Poolwise: Evaluating Reward Models for Selection across Prompts

Poolwise is a protocol that evaluates reward models for selecting training data across different prompts by choosing a fixed fraction of responses based on score and measuring the quality of the selected set with external labels. It reports within‑prompt ranking separately and shows that training each prompt’s mean score to match its average response rating improves selection over permuted or omitted mean targets in all tested seeds at 30% retention. In grouped HelpSteer experiments, the model with the highest within‑prompt accuracy selects a lower‑rated set than the correct‑mean model, and subtracting prompt means from reference responses preserves local rankings but reduces selected helpfulness for several reward models and judges. whyItMatters":"Poolwise offers a direct method to compare reward models and score transformations for data selection, addressing the limitation of existing benchmarks that only compare responses within the same prompt."

By Mateusz Modrzejewski, Tomasz Radzikowski
arXiv AI
Oct 19

Two Minds Better Than One: Collaborative Reward Modeling for LLM Alignment

The paper introduces Collaborative Reward Modeling (CRM), an online framework that uses cross-model peer review and curriculum learning to identify reliable preference pairs for training reward models (RMs). By having two RMs evaluate each other's sample selections and synchronizing their learning progress, CRM reduces the impact of noisy feedback, improving RM generalization by up to 9.94 points on RewardBench under 40% preference noise. The approach also extends to implicit-reward alignment, demonstrating robustness and broad applicability for learning from imperfect feedback.

By Jiazheng Zhang, Wenqing Jing, Zizhuo Zhang, Zhiheng Xi, Shihan Dou, Rongxiang Weng, Jiahuan Li, Jingang Wang, Mingxu Chai, Shibo Hong, Yuming Yang, Chenhao Huang, Tao Gui, Qi Zhang, Xuanjing Huang
arXiv Machine Learning
Aug 28

$p1$: Better Prompt Optimization with Fewer Prompts

The paper investigates why prompt optimization works better for some tasks than others by decomposing reward variance into response variance and system‑prompt variance. It finds that optimization succeeds when system‑prompt variance dominates, and that adding more user prompts can actually reduce this variance, especially on heterogeneous datasets. To address this, the authors propose $p1$, a filtering method that selects a small set of high‑variance user prompts, which improves optimization on reasoning benchmarks and even allows a system prompt trained on just two AIME 24 prompts to generalize well.

By Zhaolin Gao (Sid), Yu (Sid), Wang, Bo Liu, Thorsten Joachims, Kiant\'e Brantley, Wen Sun
arXiv Machine Learning
Jul 31

Personalized RewardBench: Evaluating Reward Models with Human Aligned Personalization

arXiv:2604. 07343v2 Announce Type: replace-cross Abstract: Pluralistic alignment has emerged as a critical frontier in the development of Large Language Models (LLMs), with reward models (RMs) serving as a central mechanism for capturing diverse human values.

By Qiyao Ma, Dechen Gao, Rui Cai, Boqi Zhao, Hanchu Zhou, Junshan Zhang, Zhe Zhao
arXiv Machine Learning
Oct 22

PerSPL: Personalized Semi-supervised Preference Learning

PerSPL (Personalized Semi-supervised Preference Learning) is a backbone‑agnostic framework that stabilizes cross‑prompt score coordinates using pair‑mean score centering, enabling the conversion of unlabeled responses into user‑specific training signals. It addresses the scarcity of user‑specific preference comparisons by leveraging large pools of unlabeled responses, which are otherwise unused by existing personalized reward models. Across four benchmarks—PersonalLLM, HelpSteer2, Reddit TLDR, and Chatbot Arena—PerSPL achieves the highest mean accuracy for both seen and unseen users, demonstrating its effectiveness in summarization and open‑domain chatbot interaction settings.

By Xiaoan Xu, Tingzhou Wei, Juncheng Dong, Korel Gundem, Ethan X. Fang, Zhengling Qi
arXiv Machine Learning
Sep 15

The Limits of Reference-Free Speech Quality Metrics as Evaluators and Rewards on Modern Text-to-Speech

arXiv:2609.13150v1 Announce Type: cross Abstract: Reference-free quality predictors such as UTMOS, DNSMOS and SCOREQ are the de facto automatic evaluators for text-to-speech (TTS) and are increasingl...

By Antonis Asonitis, Juan Pablo Zuluaga Gomez, Francesco Verdini, Aref Farhadipour, Marzieh Razavi, Pierre-Edouard Honnet, Vijeta Avijeet
arXiv Machine Learning
Oct 2

The Missing Coefficients: Bayesian Pairwise Merging for Model Personalization

The paper introduces Bayesian Pairwise Merging (BPM), a method that personalizes a shared expert library by inferring reward trade‑off weights from users’ pairwise choices. BPM treats these weights as latent variables, learns a posterior over them, and uses the posterior mean as merge coefficients, thereby converting natural pairwise feedback into actionable model personalization. Experiments on radiology summarization, image captioning, and story generation show BPM outperforming uniform merging and achieving high win rates with limited feedback, while also quantifying uncertainty in the inferred trade‑offs.

By Yaling Shen, Tongtong Wu, Siyuan Yan, Gholamreza Haffari