Do market crowds correct errors or amplify them through correlated beliefs?
Core argument: Markets efficiently incorporate known information through crowd wisdom, making consistent excess returns structurally difficult to achieve without an informational or analytical edge.
The ability to compare information from different markets has never been better. For example, prediction markets now offer contracts tied to key performance indicators for companies, which may provide investors with an additional way to assess the expectations embedded in stock prices. From time to time, beliefs and trading in the stock market become correlated and crowds amplify, rather than correct, errors. Steven Crist, an author and well-known handicapper, has noted that “the best friend that horseplayers have are the big race days.” The reason is that a wave of uninformed participants place bets that create a large gap between the implied and likely probability of winning. This opens an opportunity for informed handicappers to make profitable bets.

