Stock market crashes are social phenomena where external economic events combine with crowd behavior and psychology in a positive feedback loop where selling by some market participants drives more market participants to sell. Generally speaking, crashes usually occur under the following conditions: a prolonged period of rising stock prices and excessive economic optimism, a market where P/E ratios (Price-Earning ratio) exceed long-term averages, and extensive use of margin debt and leverage by market participants. Other aspects such as wars, large-corporation hacks, changes in federal laws and regulations, and natural disasters of highly economically productive areas may also influence a significant decline in the stock market value of a wide range of stocks. All such stock drops may result in the rise of stock prices for corporations competing against the affected corporations.
How Did the Stock Market Crash Affect the Banks?
By July 8, 1932, the Dow was down to 41.22. That was a 90 percent loss from its record-high close of 381.2 on September 3, 1929. It was the worst bear market in terms of percentage loss in modern U.S. history. The largest one-day percentage gain also occurred during that time. On March 15, 1933, the Dow rose 15.34 percent, a gain of 8.26 points, to close at 62.10.
What Goes up When the Stock Market Goes Down?
The mathematical description of stock market movements has been a subject of intense interest. The conventional assumption has been that stock markets behave according to a random log-normal distribution. Among others, mathematician Benoît Mandelbrot suggested as early as 1963 that the statistics prove this assumption incorrect. Mandelbrot observed that large movements in prices (i.e. crashes) are much more common than would be predicted from a log-normal distribution. Mandelbrot and others suggested that the nature of market moves is generally much better explained using non-linear analysis and concepts of chaos theory. This has been expressed in non-mathematical terms by George Soros in his discussions of what he calls reflexivity of markets and their non-linear movement. George Soros said in late October 1987, 'Mr. Robert Prechter's reversal proved to be the crack that started the avalanche'.
For example, the United States has a set of thresholds in place to guard against crashes. If the Dow Jones Industrial Average (DJIA) falls 2,400 points (threshold 2) before 1:00 p.m., the market will be frozen for an hour. If it falls below 3,600 points (threshold 3), the market closes for the day. Other countries have similar measures in place. The problem with this method today is that if one stock exchange closes, shares can often still be bought or sold in other exchanges, which can cause the preventative measures to backfire.