How Well Do Financial Markets Separate News from Noise? Evidence from an Internet Blooper
Carlos Carvalho*, Nicholas Klagge*, and Emanuel Moench
How efficiently do financial markets process news of unexpected events? This question becomes particularly salient now, as multiple events across the globe drive market movements. Do these gyrations reflect responses to fundamental news or to “noise”? In general, it is very difficult to discern how well markets process information, because there is no objective way for observers to separate fundamental news from noise components when markets react to a news report. In this post, however, we examine an unusual episode involving a false news report that provides a unique look into this question. We find that even when noise can be clearly identified, markets may take as long as a week to fully process the “signal,” or relevant information, component of news.
On September 8, 2008, a six-year-old article about the 2002 bankruptcy of United Airlines’ parent company resurfaced on the Internet and was mistakenly believed to be reporting a new bankruptcy filing by the company. This episode caused the company’s stock price to drop by as much as 76 percent in just a few minutes, before NASDAQ halted trading. After the “news” had been identified as false, the stock price rebounded, but still ended the day 11.2 percent below the previous close. Trading volumes skyrocketed during these extreme price movements. In subsequent days, the stock traded as much as 17 percent below its September 8 closing price, and on September 15 it finally traded above the price level seen just before the false news impacted the market.
… Our main findings are depicted in the chart below. It shows that after three trading sessions, United Airlines’ stock was still trading significantly below the counterfactual level implied by our model. Only on the seventh day after the episode did the stock trade at levels consistent with the absence of any residual effects attributable to the false news shock.