Daily OHLCV Data for 20 S&P 500 Equities and the CBOE Volatility Index (1982-2025)

This dataset contains daily Open, High, Low, Close, Adjusted Close, and Volume (OHLCV) records for the 20 S&P 500 equities and the CBOE Volatility Index (VIX) used in the manuscript "Multi-Dimensional Behavioral Evaluation of Agentic Stock Prediction Systems Using Large Language Model Judges with Closed-Loop Reinforcement Learning Feedback" (Al Ridhawi, Haj Ali, and Al Osman, 2026), submitted to Applied Artificial Intelligence. The records cover January 1982 through March 2025, the temporal range used for training (1982 to 2010), validation (2011 to 2016), and held-out testing (2017 to 2025) in the manuscript. Series for stocks with later initial public offering dates begin at the earliest date for which Yahoo Finance returns data. The data values were retrieved through the public Yahoo Finance interface using the yfinance Python library on the date this snapshot was generated. The underlying observations are factual market data produced by the listing exchanges. The selection of equities, temporal range, file structure, manifest, and documentation are the original curatorial contribution of the dataset authors and are released under CC BY 4.0. A README inside the archive documents file layout, source, license, and reproduction instructions.