higher than that of their particular cash stock). During the crisis this link was broken. When the futures market opened while the stock market was closed, it created a pricing imbalance: the listed price of those stocks which opened late had no chance to change from their closing price of the day before. The quoted prices were thus "stale" and did not reflect current economic conditions; they were generally listed higher than they should have been (and dramatically higher than their respective futures, which are typically higher than stocks). The decoupling of these markets meant that futures prices had temporarily lost their validity as a vehicle for price discovery; they no longer could be relied upon to inform traders of the direction or degree of stock market expectations. This had harmful effects: it added to the atmosphere of uncertainty and confusion at a time when investor confidence was sorely needed; it discouraged investors from "leaning against the wind" and buying stocks since the discount in the futures market logically implied that investors could wait and purchase stocks at an even lower price; and it encouraged portfolio insurance investors to sell in the stock market, putting further downward pressure on stock prices. The gap between the futures and stocks was quickly noted by index arbitrage traders who tried to profit through sell at market orders. Index arbitrage, a form of program trading, added to the confusion and the downward pressure on prices: Although arbitrage between index futures and stocks placed downward pressure on prices, it does not explain why the surge in sell orders that brought steep price declines began in the first place. Moreover, the markets "performed most chaotically" during those times when the links that index arbitrage program trading creates between these markets was broken. Portfolio insurance hedges Portfolio insurance is a hedging technique which attempts to manage risk and limit losses by buying and selling financial instruments (for example, stocks or futures) in reaction to changes in market price rather than changes in market fundamentals. Specifically, they buy when the market is rising, and sell when the market is falling, without regard for any fundamental information about why the market is rising or falling. Thus it is an example of an "informationless trade" that has the potential to create a market-destabilizing feedback loop. This strategy became a source of downward pressure when portfolio insurers whose computer models noted