The Feedback Effect: When Hedging Moves the Market
Every derivatives textbook makes the same quiet assumption: option trading does not affect the stock price. The stock does its random walk thing, the option value follows, and hedging is just a passive activity. But think about this. In many markets, the nominal value of options traded exceeds the value of trade in the underlying stock itself. When everyone is delta hedging, they are all buying and selling the stock in predictable amounts at predictable times. Can we really pretend this has no effect? Chapter 61 of Wilmott’s book says no, and the consequences are fascinating.