ResearchResearch paperLarge Language Models · Business, Funding & Industry1 source · Oct 19, 2026

Beyond Behavioral Accuracy: Evaluating Individual-Level Fidelity in LLM Investor Simulation

Large language models (LLMs) are increasingly used as user simulators, but can they faithfully reproduce an individual's behavior and decision logic over time?

Key points

  • We investigate this question in a longitudinal paper-trading study with 80 participants.
  • Using rolling next-day predictions, we evaluate trading activity, buy-sell structure, asset selection, and portfolio outcomes, complemented by controlled input ablations and participant-rated explanation alignment.
  • No evaluated LLM reliably outperforms a simple recent-activity persistence baseline for predicting trade occurrence, while buy-sell structure and asset selection remain difficult to reproduce.
  • These findings reveal a gap between coarse behavioral agreement and individual-level fidelity, motivating separate evaluation of behavioral accuracy, explanation alignment, and evidence dependence in personalized user simulation.

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