Regeneron's 3.72% Slide Driven by 73.84% Volume Surge Stock Ranks 137th in U.S. Trading Intensity

On September 25, 2025, Regeneron Pharmaceuticals (REGN) saw a 3.72% decline in share price amid a trading session marked by heightened liquidity. The stock accounted for $780 million in volume, a 73.84% surge from the previous day’s activity, ranking 137th in trading intensity among U.S.-listed equities. The move followed a series of strategic updates from the biotech firm, though specific catalysts for the session’s volatility remained unconfirmed in public filings.

Analysts observed that the firm’s recent pipeline developments and partnership discussions contributed to mixed investor sentiment. While long-term confidence in its therapeutic innovation remains robust, short-term positioning appeared fragmented due to evolving regulatory dynamics in key markets. Market participants noted that the stock’s performance diverged from broader sector trends, reflecting idiosyncratic factors tied to internal operational updates.

To run this back-test rigorously I need to pin down a couple of practical details: 1. Universe: Should I rank all U.S. exchange-listed common stocks each day, or focus on a particular universe (e.g., S&P 500 constituents, Russell 3000, NASDAQ only, etc.)? 2. Trade price: Do we buy at that day’s close and sell at the next day’s close, or buy at next day’s open and exit at the same day’s close? 3. Weighting: Equal-weight the 500 names each day (typical for this sort of study) or volume-weight / cap-weight? Once I have these points confirmed I can generate the data-retrieval plan and run the back-test from 2022-01-01 through the present.