arXiv Computation and Language

Item-Mean Surrogates: Why Richer Personas Fail to Deliver Individual Fidelity in LLMs as Human Surrogates

The study investigates whether large language models (LLMs) can accurately simulate individual human responses by testing the assumption that richer personas improve prediction fidelity. Across four public datasets, researchers found that LLMs largely predict item means but fail to capture individual deviations, particularly the stable, person‑by‑item signal that accounts for most variance. Even with fine‑tuning and varied models, LLMs recover only a small fraction of this nuanced signal, highlighting limitations in using them as precise human surrogates.

arXiv Computation and Language
Sep 23

Do Synthetic Personas Predict Real Audience Response? A Sim-to-Real Study Where a No-Persona Baseline Beats Persona-Based Copy Simulation

The study evaluates whether large language models (LLMs) used as synthetic personas can predict real audience responses to marketing copy. Using thousands of headline A/B tests from the Upworthy Research Archive, the authors compare a ten-persona panel grounded in real audience demographics to a no-persona zero‑shot baseline that asks the model for a typical reader’s click likelihood. Results show that the no‑persona baseline outperforms the persona‑based approach, with higher predictive validity and top‑1 accuracy, indicating that forcing the model to role‑play specific personas introduces bias and noise.

By Alexandre Cristov\~ao Maiorano
arXiv AI
Sep 4

Human Psychometric Questionnaires Mischaracterize LLM Behavior

The paper investigates whether human psychometric questionnaires can reliably characterize large language models (LLMs) in everyday interactions. By comparing eight open‑source LLMs’ value and personality profiles from Likert self‑reports (PVQ‑40/21 and BFI‑44/10) with generation probabilities on value‑laden user queries, the authors find substantial divergence between the two methods. The study shows that questionnaire items contain explicit lexical cues that lead models to respond in socially desirable ways, whereas realistic user queries lack such cues, and demographic persona prompts shift questionnaire responses but not generation outputs, indicating that questionnaire scores overestimate LLMs’ true behavioral tendencies.

By Woojung Song, Dongmin Choi, Yoonah Park, Jongwook Han, Eun-Ju Lee, Yohan Jo