Agents from the National Transportation Safety Board inspect a piece of the Boeing jetliner found in a backyard in Portland, Oregon. (Photo from the AP via the New York Times.)
What causes movements in stock prices? As we explain in Economics and Microeconomics, Chapter 8, Section 8.2 (Macroeconomics, Essentials of Economics, and Money, Banking, and the Financial System, Chapter 6, Section 6.2): “Shares of stock represent claims on the profits of the firms that issue them. As the fortunes of the firms change and they earn more or less profit, the prices of the stock the firms have issued should also change.”
We also note that: “Many Wall Street investment professionals expend a great deal of effort gathering all possible information about the future profitability of firms, hoping to buy the stocks that are most likely to rise in the future. As a result of the actions of these professional investors, all of the information about a firm that is available on news and financial websites, cable TV business shows, and online discussion sites like X and Reddit is already reflected in the firm’s stock price.” As a consequence, the price of a firm’s stock will change only as a result of new information about the future profitability of the firm issuing the stock.
During the course of a typical week, the new information that becomes available about a large company, like Apple or General Motors, is likely to indicate only minor changes in the future profitability of the firm. Therefore, we wouldn’t expect that the firm’s stock price would change very much. Sometimes, though, investors receive important new information that causes them to significantly revise their expectations of the future profitability of a firm. That’s what happened to Boeing, the jetliner manufacturer, on Friday, January 5. An Alaska Air Boeing 737 Max 9 was taking off from Portland International Airport when a piece of the plane blew out. (A Wall Street Journal article gives the details of the incident.)
The accident caused some industry observers to question whether Boeing’s quality control during manufacturing had deficiencies that might lead to other problems being discovered on the firm’s jetliners. Boeing was particularly at risk of having its quality control methods questioned because in 2019 two slightly different models of the 737 Max airliner had crashed, causing the planes to be grounded for almost two years.
The effect of the Alaska Air incident on Boeing’s stock price can be seen in the following figure, reproduced from the Wall Street Journal. On Friday, January 5 at 4 pm eastern time—the time at which trading on the New York Stock Exchange (NYSE) closes for the day—the price of Boeing’s stock was $249.00 per share. The accident took place at around 7:40 pm eastern time, so it occurred after the close of trading on the NYSE. When trading on the NYSE resumed at 9:30 am on Monday, January 8, Boeing’s stock price had declined to $227.79 per share. The size of the drop in price indicated that investors believed that the Portland accident would have a significantly negative affect on Boeing’s future profitability. Boeing’s profits could fall if the accident leads airlines to reduce their future purchases of 737 Max airliners or if Boeing’s costs rise significantly as a result of making repairs on Max airliners currently in servide or as a result of having to spend more on quality control measures when manufacturing the planes.
The effect of the Portland accident on Boeing’s stock price is an example of the efficiency of the stock market in processing information about a firm’s future profitability.
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