For instance, a stock exchange may categorize stocks in various segments depending on their risk profiles and allow limited or no trading by common investors in high-risk stocks. Derivatives, which have been described by Warren Buffett as financial weapons of mass destruction, are not for everyone as one may lose much more than they bet for. Exchanges often impose restrictions to prevent individuals with limited income and knowledge from getting into risky bets of derivatives.
There have been famous stock market crashes that have ended in the loss of billions of dollars and wealth destruction on a massive scale. An increasing number of people are involved in the stock market, especially since the social security and retirement plans are being increasingly privatized and linked to stocks and bonds and other elements of the market. There have been a number of famous stock market crashes like the Wall Street Crash of 1929, the stock market crash of 1973–4, the Black Monday of 1987, the Dot-com bubble of 2000, and the Stock Market Crash of 2008.
Sometimes, the market seems to react irrationally to economic or financial news, even if that news is likely to have no real effect on the fundamental value of securities itself. However, this market behaviour may be more apparent than real, since often such news was anticipated, and a counter reaction may occur if the news is better (or worse) than expected. Therefore, the stock market may be swayed in either direction by press releases, rumors, euphoria and mass panic.
The movements of the prices in a market or section of a market are captured in price indices called stock market indices, of which there are many, e.g., the S&P, the FTSE and the Euronext indices. Such indices are usually market capitalization weighted, with the weights reflecting the contribution of the stock to the index. The constituents of the index are reviewed frequently to include/exclude stocks in order to reflect the changing business environment.
Investing in stocks can be very costly if you trade constantly, especially with a minimum amount of money available to invest. Every time that you trade stock, either buying or selling, you will incur a trading fee. Trading fees range from the low end of $10 per trade, but can be as high as $30 for some discount brokers. Remember, a trade is an order to purchase shares in one company - if you want to purchase five different stocks at the same time, this is seen as five separate trades and you will be charged for each one.
Stocks are categorized in various ways. One way is by the country where the company is domiciled. For example, Nestlé and Novartis are domiciled in Switzerland, so they may be considered as part of the Swiss stock market, although their stock may also be traded on exchanges in other countries, for example, as American depository receipts (ADRs) on U.S. stock markets.
Such dedicated markets serve as a platform where numerous buyers and sellers meet, interact and transact. Since the number of market participants is huge, one is assured of a fair price. For example, if there is only one seller of Christmas trees in the entire city, he will have the liberty to charge any price he pleases as the buyers won’t have anywhere else to go. If the number of tree sellers is large in a common marketplace, they will have to compete against each other to attract buyers. The buyers will be spoiled for choice with low- or optimum-pricing making it a fair market with price transparency. Even while shopping online, buyers compare prices offered by different sellers on the same shopping portal or across different portals to get the best deals, forcing the various online sellers to offer the best price.
Other research has shown that psychological factors may result in exaggerated (statistically anomalous) stock price movements (contrary to EMH which assumes such behaviors 'cancel out'). Psychological research has demonstrated that people are predisposed to 'seeing' patterns, and often will perceive a pattern in what is, in fact, just noise, e.g. seeing familiar shapes in clouds or ink blots. In the present context this means that a succession of good news items about a company may lead investors to overreact positively, driving the price up. A period of good returns also boosts the investors' self-confidence, reducing their (psychological) risk threshold.
Regulation of margin requirements (by the Federal Reserve) was implemented after the Crash of 1929. Before that, speculators typically only needed to put up as little as 10 percent (or even less) of the total investment represented by the stocks purchased. Other rules may include the prohibition of free-riding: putting in an order to buy stocks without paying initially (there is normally a three-day grace period for delivery of the stock), but then selling them (before the three-days are up) and using part of the proceeds to make the original payment (assuming that the value of the stocks has not declined in the interim).