`Thirty-two percent of Americans who were invested in the stock market during at least one of the last five financial downturns pulled some or all of their money out of the market. That’s according to a NerdWallet-commissioned survey, which was conducted online by The Harris Poll of more than 2,000 U.S. adults, among whom over 700 were invested in the stock market during at least one of the past five financial downturns, in June 2018. The survey also found that 28% of Americans would not keep their money in the stock market if there were a crash today.`

### In France, the main French stock index is called the CAC 40. Daily price limits are implemented in cash and derivative markets. Securities traded on the markets are divided into three categories according to the number and volume of daily transactions. Price limits for each security vary by category. For instance, for the more[most?] liquid category, when the price movement of a security from the previous day's closing price exceeds 10%, the quotation is suspended for 15 minutes, and transactions are then resumed. If the price then goes up or down by more than 5%, transactions are again suspended for 15 minutes. The 5% threshold may apply once more before transactions are halted for the rest of the day. When such a suspension occurs, transactions on options based on the underlying security are also suspended. Further, when more than 35% of the capitalization of the CAC40 Index cannot be quoted, the calculation of the CAC40 Index is suspended and the index is replaced by a trend indicator. When less than 25% of the capitalization of the CAC40 Index can be quoted, quotations on the derivative markets are suspended for half an hour or one hour, and additional margin deposits are requested.[43]

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.

**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.[9] Among others, mathematician Benoît Mandelbrot suggested as early as 1963 that the statistics prove this assumption incorrect.[10] 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.[11] 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.[12] George Soros said in late October 1987, 'Mr. Robert Prechter's reversal proved to be the crack that started the avalanche'.[13][14]**

# Which Is the Best Stock Market in World?

##### In France, the main French stock index is called the CAC 40. Daily price limits are implemented in cash and derivative markets. Securities traded on the markets are divided into three categories according to the number and volume of daily transactions. Price limits for each security vary by category. For instance, for the more[most?] liquid category, when the price movement of a security from the previous day's closing price exceeds 10%, the quotation is suspended for 15 minutes, and transactions are then resumed. If the price then goes up or down by more than 5%, transactions are again suspended for 15 minutes. The 5% threshold may apply once more before transactions are halted for the rest of the day. When such a suspension occurs, transactions on options based on the underlying security are also suspended. Further, when more than 35% of the capitalization of the CAC40 Index cannot be quoted, the calculation of the CAC40 Index is suspended and the index is replaced by a trend indicator. When less than 25% of the capitalization of the CAC40 Index can be quoted, quotations on the derivative markets are suspended for half an hour or one hour, and additional margin deposits are requested.[43]

*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]*