that stocks opened lower and continued their steep price decline. The models recommended even further sales. The potential for computer-generated feedback loops that these hedges created has been discussed as a factor compounding the severity of the crash, but not as an initial trigger. Economist Hayne Leland argues against this interpretation, suggesting that the impact of portfolio hedging on stock prices was probably relatively small. Similarly, the report of the Chicago Mercantile Exchange found the influence of "other investors—mutual funds, broker-dealers, and individual shareholders—was thus three to five times greater than that of the portfolio insurers" during the crash. Numerous econometric studies have analyzed the evidence to determine whether portfolio insurance exacerbated the crash, but the results have been unclear. Markets around the world that did not have portfolio insurance trading experienced as much turmoil and loss as the U.S. market. More to the point, the cross-market analysis of Richard Roll, for example, found that markets with a greater prevalence of computerized trading (including portfolio insurance) actually experienced relatively less severe losses (in percentage terms) than those without. Noise trading Contemporaneous causality and feedback behavior between markets increased dramatically during this period. In an environment of increased volatility, confusion and uncertainty, investors not only in the US but also across the world were inferring information from changes in stock prices and communication with other investors in a self-reinforcing contagion of fear. This pattern of basing trading decisions largely on market psychology is often referred to as one form of "noise trading", which occurs when ill-informed investors "[trade] on noise as if it were news". A significant amount of trading takes place based on information which is unquantifiable and potentially irrelevant, such as unsubstantiated rumors or a "gut feeling",. Investors vary between seemingly rational and irrational behaviors as they "struggle to find their way between the give and take, between risk and return, one moment engaging in cool calculation and the next yielding to emotional impulses". If noise is misinterpreted as meaningful news, then the reactions of risk-averse traders and arbitrageurs will bias the market, preventing it from establishing prices that accurately reflect the fundamental state of the underlying stocks. For example, on October 19 rumors that the New York Stock Exchange would close created additional confusion and drove prices further downward, while rumors the next day that two Chicago Mercantile Exchange clearinghouses were insolvent deterred some investors from trading in