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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:[1] 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.
One mitigation strategy has been the introduction of trading curbs, also known as "circuit breakers", which are a trading halt in the cash market and the corresponding trading halt in the derivative markets triggered by the halt in the cash market, all of which are affected based on substantial movements in a broad market indicator. Since their inception, circuit breakers have been modified to prevent both speculative gains and dramatic losses within a small time frame.[43]

Why Do Stock Market Crashes Happen?


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Money Morning gives you access to a team of ten market experts with more than 250 years of combined investing experience – for free. Our experts – who have appeared on FOXBusiness, CNBC, NPR, and BloombergTV – deliver daily investing tips and stock picks, provide analysis with actions to take, and answer your biggest market questions. Our goal is to help our millions of e-newsletter subscribers and Moneymorning.com visitors become smarter, more confident investors.

How Do I Own a Stock?


Research at the Massachusetts Institute of Technology suggests that there is evidence the frequency of stock market crashes follows an inverse cubic power law.[15] This and other studies such as Prof. Didier Sornette's work suggest that stock market crashes are a sign of self-organized criticality in financial markets.[16] In 1963, Mandelbrot proposed that instead of following a strict random walk, stock price variations executed a Lévy flight.[17] A Lévy flight is a random walk that is occasionally disrupted by large movements. In 1995, Rosario Mantegna and Gene Stanley analyzed a million records of the S&P 500 market index, calculating the returns over a five-year period.[18] Researchers continue to study this theory, particularly using computer simulation of crowd behaviour, and the applicability of models to reproduce crash-like phenomena.
Having been suspended for three successive trading days (October 9, 10, and 13), the Icelandic stock market reopened on 14 October, with the main index, the OMX Iceland 15, closing at 678.4, which was about 77% lower than the 3,004.6 at the close on October 8. This reflected that the value of the three big banks, which had formed 73.2% of the value of the OMX Iceland 15, had been set to zero.
Research at the Massachusetts Institute of Technology suggests that there is evidence the frequency of stock market crashes follows an inverse cubic power law.[15] This and other studies such as Prof. Didier Sornette's work suggest that stock market crashes are a sign of self-organized criticality in financial markets.[16] In 1963, Mandelbrot proposed that instead of following a strict random walk, stock price variations executed a Lévy flight.[17] A Lévy flight is a random walk that is occasionally disrupted by large movements. In 1995, Rosario Mantegna and Gene Stanley analyzed a million records of the S&P 500 market index, calculating the returns over a five-year period.[18] Researchers continue to study this theory, particularly using computer simulation of crowd behaviour, and the applicability of models to reproduce crash-like phenomena.
In 1907 and in 1908, the NYSE fell by nearly 50% due to a variety of factors, led by the manipulation of copper stocks by the Knickerbocker company.[21] Shares of United Copper rose gradually up to October, and thereafter crashed, leading to panic.[22][23] A number of investment trusts and banks that had invested their money in the stock market fell and started to close down. Further bank runs were prevented due to the intervention of J. P. Morgan.[24] The panic continued to 1908 and led to the formation of the Federal Reserve in 1913.[25]

Since the crashes of 1929 and 1987, safeguards have been put in place to prevent crashes due to panicked stockholders selling their assets. Such safeguards include trading curbs, or circuit breakers, which prevent any trade activity whatsoever for a certain period of time following a sharp decline in stock prices, in hopes of stabilizing the market and preventing it from falling further.


It’s likely some of these Americans might rethink pulling their money if they knew how quickly a portfolio can rebound from the bottom: The market took just 13 months to recover its losses after the most recent major sell-off in 2015. Even the Great Recession — a devastating downturn of historic proportions — posted a complete market recovery in just over five years. The S&P 500 then posted a compound annual growth rate of 16% from 2013 to 2017 (including dividends).
Money Morning gives you access to a team of ten market experts with more than 250 years of combined investing experience – for free. Our experts – who have appeared on FOXBusiness, CNBC, NPR, and BloombergTV – deliver daily investing tips and stock picks, provide analysis with actions to take, and answer your biggest market questions. Our goal is to help our millions of e-newsletter subscribers and Moneymorning.com visitors become smarter, more confident investors.

What Ended the Recession in 2009?


Research at the New England Complex Systems Institute has found warning signs of crashes using new statistical analysis tools of complexity theory. This work suggests that the panics that lead to crashes come from increased mimicry in the market. A dramatic increase in market mimicry occurred during the whole year before each market crash of the past 25 years, including the recent financial crisis. When investors closely follow each other's cues, it is easier for panic to take hold and affect the market. This work is a mathematical demonstration of a significant advance warning sign of impending market crashes.[19][20]
If you’ve gone with a “set it and forget it” strategy — like investing in a target-date retirement fund, as many 401(k) plans allow you to do, or using a robo-advisor — diversification already is built in. In this case, it’s best to sit tight and trust that your portfolio is ready to ride out the storm. You’ll still experience some painful short-term jolts, but this will help you avoid losses from which your portfolio can’t recover.
The following day, Black Tuesday, was a day of chaos. Forced to liquidate their stocks because of margin calls, overextended investors flooded the exchange with sell orders. The Dow fell 30.57 points to close at 230.07 on that day. The glamour stocks of the age saw their values plummet. Across the two days, the Dow Jones Industrial Average fell 23%.
Meanwhile, those who are most concerned with corporate coffers, the chief financial officers (CFOs), are the least optimistic about the U.S. economy and, by extension, the stock market. Almost half (48.6%) of CFOs surveyed believe that the U.S. will fall into a recession in 2019, and a whopping 82% of them believe that a recession will occur in 2020. (Source: “Recession Considered Likely By Year-End 2019,” Duke CFO Global Business Outlook, last accessed March 14, 2019.)
Ideally, at the start of your investment journey, you did risk profiling. If you skipped this step and are only now wondering how aligned your investments are to your temperament, that’s OK. Measuring your actual reactions during market agita will provide valuable data for the future. Just keep in mind that your answers may be biased based on the market’s most recent activity.
Markets can also be stabilized by large entities purchasing massive quantities of stocks, essentially setting an example for individual traders and curbing panic selling. However, these methods are not only unproven, they may not be effective. In one famous example, the Panic of 1907, a 50 percent drop in stocks in New York set off a financial panic that threatened to bring down the financial system. J. P. Morgan, the famous financier and investor, convinced New York bankers to step in and use their personal and institutional capital to shore up markets.
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