American Shares Plunge 30.91% in Volume, Drop to 491st Rank as Regulatory Scrutiny and Market Shifts Weigh

American shares closed with a volume of $0.23 billion on September 25, 2025, representing a 30.91% decline from the previous day's trading activity. The stock ranked 491st in terms of trading volume among listed equities, while American International Group (AIG) fell 1.03% during the session.

Recent developments highlight a mixed market environment for American. Regulatory scrutiny over corporate governance practices has intensified, with analysts noting potential implications for investor sentiment. Additionally, a shift in industry dynamics, including supply chain adjustments and evolving consumer demand patterns, has created uncertainty around near-term earnings visibility. These factors, combined with broader macroeconomic headwinds, have contributed to a cautious stance among institutional investors.

Back-testing parameters for a 500-stock portfolio strategy require defining key operational constraints. The universe selection must specify whether to include the full U.S. equity market or focus on the Russell 3000. Rebalancing protocols need clarification—specifically, whether to equally weight holdings daily and execute trades at open/close for a one-day holding period. Transaction cost assumptions, such as flat fees or slippage adjustments, will also influence performance metrics. Data efficiency can be optimized by using standardized universes and automating OHLCV data aggregation to avoid redundant queries.

Proposed implementation involves three steps: 1) Define the investable universe (e.g., Russell 3000), 2) Equal-weight the top 500 by volume daily, and 3) Execute rebalancing at the next day's open with full exit at close. This approach balances practicality with analytical rigor. Confirmation of these assumptions is required before initiating data collection and back-testing from January 3, 2022, to the current date.