WESTLAKE, Texas--(BUSINESS WIRE)--Schwab today introduced the Schwab Trading Activity Index (STAX), offering timely insights into retail trading behavior from one of the industry’s largest retail investor client bases. Building on the success of the TD Ameritrade Investor Movement Index® (IMXSM), launched in 2013, the STAX is a new proprietary, behavior-based index that analyzes retail investor stock positions and trading activity to illuminate what investors were actually doing and how they were positioned ...