The stock index is the stock price index. It is a reference index compiled by stock exchanges or financial services institutions to indicate changes in the stock market. Due to the volatility of stock prices, investors are bound to face market price risks. It is easy for investors to know the price changes of a specific stock, but it is neither easy nor annoying to know the price changes of various stocks one by one. In order to adapt to this situation and need, some financial service institutions make use of their professional knowledge and the advantages of being familiar with the market to compile stock price indexes and publish them publicly as indicators of market price changes. Based on this, investors can test the effect of their investment and predict the trend of the stock market. At the same time, the press, company bosses and even political leaders also use this as a reference index to observe and predict the social, political and economic development situation.

This stock index, that is, the average price indicating the changes in the stock market. Prepare a stock index, usually in a certain

Take the month of the year as the benchmark, take the stock price of the base period as 100, compare the stock prices of subsequent periods with the base period price, and calculate the percentage of rise and fall, which is the stock index of this period. Investors can judge the trend of stock price according to the rise and fall of the index. And in order to reflect the trend of the stock market to investors in real time, almost all stock markets will announce the stock price index at the same time as the stock price changes.

There are three factors to be considered in calculating the stock index: first, sampling, that is, extracting a few representative constituent stocks from many stocks; The second is weighted, weighted average by unit price or total value, or unweighted average; The third is a calculation program, which calculates arithmetic average, geometric average, or considers price and total value.

Because there are many kinds of listed stocks, it is an arduous and complicated task to calculate the average price or index of all listed stocks, so people often choose a few representative sample stocks from listed stocks and calculate the average price or index of these sample stocks. Used to indicate the general trend and fluctuation range of stock prices in the whole market. When calculating the average or index of stock price, the following four points are often considered: (1) sample stocks must be typical and common. Therefore, the factors such as industry distribution, market influence, stock grade and appropriate quantity should be considered comprehensively when selecting sample correspondence. (2) The calculation method should have high adaptability, and can make corresponding adjustments or corrections to the rapidly changing stock market, so that the stock index or average value has good sensitivity. (3) There should be scientific calculation basis and means. The calculation basis must be unified, generally based on the closing price, but with the increase of calculation frequency, some are calculated at the hourly price or even shorter time. (4) The base period should be well balanced and representative.

Second, the calculation method of index

When calculating the stock index, the stock index and the average price of the stock are often calculated separately. By definition, the stock index is the average share price. However, as far as their actual impact on the stock market is concerned, the average share price is an overall level reflecting the changes of various stock prices, which is usually expressed as an arithmetic average. By comparing the average stock prices in different periods, people can know the changes of various stock prices. Stock index is a relative index that reflects the changes of stock prices in different periods, that is, the percentage of the average stock price in the first period as the benchmark of the average stock price in another period. Through the stock index, people can know the percentage of stock price rising or falling relative to the base stock price during the calculation period. Because the stock index is a relative index, it can measure the change of stock price more accurately than the average stock price in a long period of time.

1. Calculation of average share price

The average stock price reflects the absolute level of listed stock prices at a certain moment, which can be divided into three categories: simple arithmetic stock price average, revised stock price average and weighted stock price average. People can see the changes and trends of stock prices by comparing the average stock prices at different times.

(1) simple arithmetic stock price average

Simple arithmetic stock price average is obtained by dividing the sum of daily closing prices of sample stocks by the number of samples, namely:

Simple arithmetic average stock price = (P 1+P2+P3+…+PN)/n

The average share price in the world is the first-Dao? Jones' average share price was calculated by simple arithmetic average method before 1928 65438+ 10/month.

Now suppose that four stocks, A, B, C and D, are sampled from a stock market, and the closing prices on a certain trading day are 10 yuan, 16 yuan, 24 yuan and 30 yuan, respectively, to calculate the average stock price of this market. Substituting the above figures into the formula, we get:

Average share price = (P 1+P2+P3+P4)/n

=( 10+ 16+24+30)/4

= 20 (yuan)

Although the simple arithmetic of stock price average is simple, it has two shortcomings: First, the weight of various sample stocks is not considered, so it is impossible to distinguish the different effects of sample stocks with different importance on stock price average. Second, when the sample shares distribute bonus shares and increase capital in share split, the average share price will break and lose continuity, which makes it difficult to compare the time series before and after. For example, if the above-mentioned D shares are split into three shares with 1 share, the share price will inevitably be lowered from 30 yuan to 10 yuan. The average value at this time is (10+16+24+10)/4 =15. That is to say, due to the technical changes in the D-share division, the average share price has dropped from 20 yuan to 15 yuan (this has not taken into account other factors affecting the stock price changes), which obviously does not meet the requirements of taking the average as an indicator to reflect the stock price changes.

(2) The average number of shares after revision.

There are two revised average stock prices:

One is divisor correction method, also called track correction method. This is the American way? A method of calculating the average stock price created by Jones in 1928. The core of this method is to find a constant divisor, so as to correct the changes of the average share price caused by stock split, capital increase, bonus and other factors, and maintain the continuity and comparability of the average share price. The specific method is to divide the new total share price by the old average share price to find a new divisor, and then divide the total share price in the calculation period by the new divisor to get the revised average share price. Namely:

New dividing line = changed new total share price/old average share price

Revised average share price = total share price in the reporting period/new divisor

In the above example, the divisor is 4, and the adjusted new divisor should be:

New divisor = (10+16+24+10)/20 = 3. If the new divisor is substituted into the following formula, then:

The average value of the revised stock price = (10+16+24+10)/3 = 20 (yuan) is the same as that calculated when it is not divided, and the stock price level will not change due to stock split.

The second is the stock price correction method. The stock price correction method is to restore the stock price after stock breakdown and other changes to the stock price before the change, so that the average stock price remains unchanged. The average value of 500 stock prices compiled by The New York Times, USA, is calculated by the stock price correction method.

(3) Weighted average share price

The weighted average stock price is the average stock price calculated by weighted average according to the relative importance of various sample stocks, and its weight (Q) can be the number of trading stocks, the total market value of stocks, the stock circulation, etc.

2. Calculation of stock index

Stock index is a relative index reflecting the changes of stock prices at different time points. Usually, the stock price in the reporting period is compared with the fixed base period price, and the ratio of the two is multiplied by the index value of the base period, which is the stock index in the reporting period. There are three methods to calculate stock index: one is relative method, the other is comprehensive method, and the third is weighting method.

(1) relative method

The relative method, also known as the average method, is to calculate the stock index of each sample first. Add up and get the arithmetic average of the total. Its calculation formula is:

Stock index = sum of n sample stock indexes /n

British economists use this method to calculate the common stock index.

(2) Comprehensive method

The comprehensive method is to add the base period and reporting period prices of sample stocks respectively, and then compare them to get the stock index. Namely:

Stock index = sum of stock prices in the reporting period/sum of stock prices in the base period.

Substitution number:

Stock price index = (8+12+18)/(5+8+10+15) = 52/38 =136.8.

That is, the share price in the reporting period rose by 36.8% compared with the base period.

Judging from the calculation of stock index by average method and comprehensive method, the factors such as the different circulation and trading volume of various sample stocks and the different influence on the stock price of the whole stock market are not taken into account, so the calculated index is not accurate enough. In order to accurately calculate the stock index, it is necessary to add weight, which can be either volume or circulation.

(3) Weighting method

The weighted stock index is weighted according to the relative importance of sample stocks in each period, and its weight can be the number of shares traded and the stock circulation. According to the time division, the weight can be the number of basic options or the number of reported options. The index weighted by the number of shares traded in the base period (or circulation disk) is called Rasbel index; An index weighted by the number of stocks traded (or circulated) during the reporting period is called the quotation index.

Rasbell index focuses on the number of shares traded in the base period (or circulation), while Paixu index focuses on the number of shares traded in the reporting period (or circulation). At present, most stock indexes in the world are Pais indexes.

Third, stock index and investment income.

The stock index is a proportional function of the market value of the index portfolio, and its fluctuation range is the return rate of this portfolio. However, in the calculation of the stock index, the transaction cost of the stock is not deducted, so the actual income of investors will be less than the fluctuation range of the stock index, that is, the maximum return on investment of the index portfolio.

There is often a proverb circulating in the stock market, which is called "the cow earns the bear's compensation", that is to say, investors make profits in the bull market and lose money in the bear market, but if they are analyzed as an investment as a whole, they may not be profitable in the bull market.

1. If the bull market is reversible, investors will only lose money instead of making money. The midpoint of China Shanghai Stock Exchange Index is around 600 points. In the bull market of 1993, the Shanghai stock market once broke through 1500 points, and then fell back to more than 300 points in July of 1994. 1September 1994, the Shanghai stock market rushed to 1000, but soon fell below 600. Judging from the index operation in recent years, the Shanghai Composite Index always starts below 600 points, and then returns to 600 points after forming a bull market. It can be said that all bull markets in Shanghai are reversible.

When the Shanghai Composite Index rushes from 600 points to 1000 points and returns to its original place, there may be gains and losses for individual investors, and wealth will be transferred between them. But for this group of investors, they will not only gain nothing, but also lose something.

First, at any time, investors have to pay transaction tax and handling fee. The stock index rose from 600 points and then returned to 600 points. For investors as a whole, there is no return on investment except transaction costs. However, the trading volume of Shanghai stock market above this point should account for at least half of the total trading volume. For investors, it is futile to spend more than half of the handling fee and transaction tax, because the purpose of investing in stocks is to find ways to get benefits from the stock rise.

Secondly, investors paid extra price for the rights issue and the issuance of new shares. Rights issue and new share issue always refer to the price in the secondary market. The higher the share price in the secondary market, the higher the issue price. When the index returns to below 600 points, it is equivalent to lock-in for shareholders who issue shares or new shares above this point, which is different from the lock-in of the secondary market, because the lock-in of the secondary market is only a change of hands between shareholders, and there is no loss of funds. However, after the high-priced rights issue or subscription of new shares, the funds will flow to listed companies, which is a huge loss for shareholders as a whole. For example, when Tsingtao Brewery was issued, its cost per share was about 12.8 yuan, but its net asset per share was only 2 yuan. That is to say, regardless of the opening price of the stock, shareholders only bought 2 yuan's net assets at the cost of 12.8 yuan. If investors invest in national debt or deposit the money from Tsingtao Brewery, they can get at least 1.3 yuan's income every year. However brilliant Tsingtao Brewery is, it is difficult for the average annual income to reach such a high level. Therefore, for a reversible bull market, investors as a whole only lose money.

Even in a big bull market, investors may not be profitable. The fluctuation range of the stock index is the investor's return on investment, but this return on investment is nominal without deducting the transaction cost. For some mature stock markets in the west, because their annual turnover rate is generally only about 30%, their transaction costs can generally be ignored. In China's stock market, due to the frequent turnover of shareholders, the turnover rate in recent two years is generally around 700. If transaction costs are included, China's shareholder income is actually negative.

1994, the tradable shares in Shanghai and Shenzhen stock markets have generated nearly 5 billion yuan of after-tax profits for shareholders, but the total turnover of these two stock markets this year is as high as 820 billion yuan. According to the transaction tax of 3I and the handling fee of nearly 4.5I, shareholders will spend a total of/kloc-0.2 billion yuan in transaction costs. Compared with revenue and expenditure, shareholders have to pay 7 billion yuan.

Although the composite index of Shanghai and Shenzhen stock markets is much higher than the base of 100 at the beginning of counting, according to preliminary calculation, by the end of 1995, the after-tax profits created by listed companies in Shanghai and Shenzhen stock markets in five years only in the secondary market reached 100 billion yuan, and the transaction fees and taxes paid by shareholders at this stage reached as high as 20 billion yuan.

Compared with 1990, although the Shanghai and Shenzhen stock markets are still bull markets, the shareholders as a whole are losing money, because the returns given by listed companies can hardly offset the cost of stock trading.

3. If the bull market makes the stock price deviate from its investment value, then the shareholders' profits are virtual, and some shareholders' profits are based on the losses of others. In a short-term bull market, the stock market may create an illusion that all shareholders are profitable, but this kind of profit is fictitious, because the overall value of stocks is calculated by the transaction price of some stocks. When a stock is traded at a higher price, the market value of some unlisted stocks will be calculated at the trading price. As a result, the book value of shareholders holding such shares has increased. For example, more than 70% of the state-owned shares or legal person shares of listed companies in China are not listed and circulated, but some people often calculate the value of state-owned assets based on the market price of stocks, and after the stock price rises, they think that state-owned assets have increased in value. However, if all the shares of listed companies are in circulation, it is difficult for the stock price to be as high as the current stock market due to the sharp increase in stock supply. Therefore, the profit in the stock market can not be calculated by the transaction price of others, but only by the transaction price realized when selling. In addition, when the stock price deviates from its investment value, the profits of some shareholders are based on the losses of other shareholders. If the annual after-tax profit of a stock is 0. 1 yuan and the current one-year savings rate is 10%, the theoretical price of this stock should be 1 yuan. When some investors speculate the price so wildly that it deviates from the investment value, for example, they speculate the price from 1 yuan to 5 yuan, and 1 yuan buys 5 yuan and sells it, making a profit for 4 yuan and 5 yuan, and losing 4 yuan, because the actual income of this stock is only equivalent to 1 yuan's savings deposit. Therefore, in stock trading, it is generally the return after buying, and new investors return to old investors.

Four, several famous stock indexes in the world

Dow Jones stock index

The Dow Jones stock index is the oldest stock index in the world, and its full name is the average stock price. Prepared by charles dow, founder of Dow Jones Company, on 1884. Its original Dow Jones stock price average index is based on 1 1 representative railway companies, which is calculated and compiled by arithmetic average method and published in the Daily Communication edited and published by charles dow himself. Its calculation formula is:

Average share price = the sum of the prices of the selected stocks. Starting from 1897, the Dow Jones average stock price index is divided into two categories: industry and transportation, in which the industrial average stock price index includes 12 stocks and the transportation average index includes 20 stocks, which are published in the Wall Street Journal published by Dow Jones Company. 1929, the Dow Jones stock price average index added utility stocks, making it include 65 stocks, which have continued to this day.

At present, the average Dow Jones stock price index is based on 1928 65438+ 10/month. Because the average price of Dow Jones stock at the close of this day is about 100, it is set as the benchmark date. In the future, the percentage calculated by comparing the stock price with the benchmark date becomes the voting price index of each period, so the current stock index is generally based on points, and the rise and fall of each point of the stock index is the percentage of the rise and fall relative to the benchmark date.

The initial calculation method of Dow Jones stock price average index is simple arithmetic average method. When the stock is ex-dividend, the stock index will be discontinuous. After 1928, the Dow Jones stock average price index was changed to a new calculation method, that is, the connection technology was adopted when the stock was ex-dividend or ex-dividend, so as to ensure the continuity of the stock index, make the stock index more perfect and gradually spread to the whole world.

At present, the Dow Jones stock price average index is divided into four groups. The first group is the average index of industrial stock prices. It is composed of 30 representative stocks of large industrial and commercial companies, which become larger with the development of economy, and can roughly reflect the price level of the entire industrial and commercial stocks in the United States, which is also the average price of Dow Jones Industrial Stock that people usually quote. The second group is the average stock price index of the transportation industry.

Including the shares of 20 representative transportation companies, namely, 8 railway transportation companies, 8 airlines and 4 road freight companies. The third group is the average share price index of public utilities, which consists of 1 5 stocks of gas companies and power companies representing American public utilities. The fourth group is the average price composite index.

It is a comprehensive index composed of 65 stocks in the first three groups of stock price average indexes. Although this group of comprehensive indexes provides direct stock market conditions for dominant stocks, the first group-industry stock price average index is usually cited now.

Dow Jones average stock price index is the most influential and authoritative stock price index in the world at present. One of the reasons is that the stocks selected by the Dow Jones average share price index are representative, and the issuing companies of these stocks are all famous companies with important influence in the industry. Their share prices have attracted the attention of the world stock market, and investors from all countries attach great importance to them. In order to maintain this feature, Dow Jones often adjusts the stocks selected by its stock price average index, and replaces those stocks that lose their representativeness with dynamic and more representative company stocks. Since 1928, 30 kinds of industrial and commercial company stocks used only to calculate the average price index of Dow Jones Industrial Average have been replaced 30 times. Almost every two years, the stock of a new company will replace the stock of the old company. The second reason is that The Wall Street Journal, the news media that publishes the Dow Jones stock price average index, is the most influential newspaper in the world financial circle.

The newspaper reported in detail the average index, percentage change rate of each sample stock and the turnover of each sample stock calculated every hour every day, and paid attention to the stock price average index after share split's correction. During the business hours of the new york Stock Exchange, the Dow Jones average stock price index is published every half hour. The third reason is that this average stock price index has never stopped since its compilation, and it can be used to compare the stock market and economic development in different periods. It has become one of the most sensitive average stock price indexes reflecting the changes in the American stock market, and it is the main reference for observing market dynamics and engaging in stock investment. Of course, because dow jones stock price indexes is a constituent stock index, its representativeness has been questioned and criticized by people, because it only includes a very small part of more than 2,500 listed companies, and most of them are active stocks, excluding companies in the service industry and financial industry that have developed rapidly in recent years.

Standard & Poor's stock price index

In addition to dow jones stock price indexes, the Standard & Poor's share price index is also very influential in the United States. It is the stock price index compiled by Standard & Poor's Company, the largest securities research institution in the United States. The company began to compile and publish the stock price index on 1923. Initially, 230 stocks were selected and two stock price indices were compiled. By 1957, the range of this stock price index has expanded to 500 stocks, divided into 95 combinations. The four most important groups are industrial group, railway group, public utility group and 500-share mixed group. From 1 July 9761,it was changed to 400 industrial stocks, 20 transportation stocks, 40 public utilities stocks and 40 financial stocks. For decades, although the stock has changed, it has always remained at 500. Standard & Poor's stock price index is based on the average market price of sample stocks from 194 1 to 1943, weighted by the number of listed stocks, and weighted by the base period, and its base is 10. Take the current stock market price multiplied by the number of shares issued in the stock market as the numerator, the base stock market price multiplied by the number of shares in the base period as the denominator, and the divided number multiplied by 10 as the stock price index.

New york Stock Exchange Stock Price Index

Stock price index of new york Stock Exchange. This is the stock price index compiled by new york Stock Exchange. Since June, 1966. First, the common stock price index was changed to a mixed index, including 1570 stocks of 1500 companies listed on new york Stock Exchange. The specific calculation method is to arrange these stocks according to the price level, and calculate the price indexes of industrial stocks, financial stocks, public utilities stocks and transportation stocks respectively. The largest and most extensive is the industrial stock price index, which consists of 1093 stocks; The financial stock index includes 223 stocks including investment companies, savings and loan associations, installment financing companies, commercial banks, insurance companies and real estate companies. The stock price index of transportation industry includes 65 stocks of railway, aviation, ship and automobile companies; The stock price index of public utilities includes shares of telephone and telegraph company, gas company, electric power company and post and telecommunications company 189.

New york's stock price index is based on196565438+50 points determined on February 3 1 day, and adopts the form of comprehensive index. The new york Stock Exchange announces the changes of the index every half hour. Although new york Stock Exchange has not compiled a stock price index for a long time, it is welcomed by investors because it can comprehensively and timely reflect the comprehensive situation of its stock market activities.

Nikkei Jones stock index (Nikkei average share price)

It is the average stock price compiled and published by Japan Economic News Agency, which reflects the price changes of Japanese stock market. The index was compiled from September 1950.

Initially, the revised average share price was calculated based on the shares of 225 companies listed on the first market of Tokyo Stock Exchange, which was then called "Zhengdong revised average share price". On may 1975 and may 1 day, the nihon keizai shimbun bought a trademark from Dow Jones, and calculated it with the correction method of Dow Jones. The stock index was renamed "Nikkei Jones Average Share Price". 1 985 may1day, when the contract expires 10 year, the name was changed to "Nikkei average share price" through negotiation between the two companies.

According to the sample number of the calculation object, the index is divided into two types, one is the average price of 225 Nikkei stocks. The selected samples are all stocks listed in the primary market of Tokyo Stock Exchange, and will not change in principle after the samples are selected. 198 1 year, manufacturing enterprises 150, construction enterprises 10, aquaculture enterprises 3, mining enterprises 3, commerce enterprises 12, road transport and maritime transport enterprises 14, finance and finance. Because the average share price of 225 Nikkei stock indexes has been continuous from 1950, its continuity and comparability are good, and it has become the most commonly used and reliable index to investigate and analyze the long-term evolution and dynamics of Japanese stock market. Another index is the average share price of the Nikkei 500 index. This is compiled by 1982 1.4. Because its sample includes 500 kinds of stocks, its representation is relatively broader, but its sample is not fixed. In April each year, samples are changed according to the operating conditions, transaction volume, transaction amount and total market value of listed companies.

Financial Times Stock Price Index

The full name of the Financial Times stock price index is "London Financial Times Industrial and Commercial Common Stock Price Index", which is published by the Financial Times. The stock price index includes 30 representative publicly listed common stocks selected from British industry and commerce. It takes 1 935 July1as the base period, and its base point is 100. The stock price index is famous for showing the London stock market in time.

Hong kong hang seng index

Hong Kong Hang Seng Index is the oldest and most influential stock price index in Hong Kong stock market. Promulgated by Hang Seng Bank of Hong Kong on June 24th, 1969 165438.

The Hang Seng Stock Index consists of 33 representative and economically powerful stocks selected from more than 500 listed companies in Hong Kong, which are divided into four categories-4 financial stocks, 6 public utility stocks, 9 real estate stocks and 65,438+04 other industrial and commercial stocks (including aviation and hotels).

These stocks account for 63.8% of the market value of Hong Kong stocks, because the stock index involves various industries in Hong Kong and is very representative.

The compilation of Hang Seng Stock Index is based on July 3 1, 1, 964, because the Hong Kong stock market operated normally on this day, and the turnover value was even, which can reflect the basic situation of the whole Hong Kong stock market. The base point is determined as 100 point. The calculation method is to multiply the daily closing price of 33 kinds of stocks by their respective issued shares as the market value of the calculation day, then compare it with the market value of the base period, and then multiply it by 100 to get the stock price index of the day.

Because the base period selected by Hang Seng Stock Index is appropriate, the Hang Seng Stock Index can basically reflect the activity of the whole stock market, whether the stock market is in a big ups and downs or at a normal trading level.

Hang Seng Stock Price Index has been adjusted several times since it was published in 1969. Since the Hong Kong authorities passed legislation in August and 1980 merged the Hong Kong Stock Exchange, the Far East Stock Exchange, the Gold and Silver Stock Exchange and the Kowloon Stock Exchange into the Hong Kong Stock Exchange, at present, only the Hang Seng Stock Index coexists with the newly generated Hong Kong Index, and all other stock indexes in Hong Kong no longer exist.

China stock index

1. Shanghai Composite Index is a stock index compiled by Shanghai Stock Exchange and officially released on 1990 12 19. The sample of the stock index is all the stocks listed on the Shanghai Stock Exchange, and the newly listed stocks are included in the calculation range of the stock index on the second day of listing.

The weight of stock index is the total share capital of listed companies. Because the shares of listed companies in China are divided into tradable shares and non-tradable shares, and their tradable shares are not consistent with the total share capital, the stocks with larger total share capital have a greater impact on the stock index. The Shanghai Composite Index often becomes a tool for large institutions to make the market, which makes the trend of the stock index deviate from the rise and fall of most stocks.

The release of the Shanghai Stock Exchange's stock index is almost synchronized with the changes in the stock market, which is an indispensable reference for China investors and securities practitioners to judge the trend of stock price changes.

2. Shenzhen Composite Index is a stock index compiled by Shenzhen Stock Exchange, and the base period is1991April 3. The calculation method of stock index is basically the same as that of Shanghai Stock Exchange. The sample is all the stocks listed on Shenzhen Stock Exchange, and the weight is the total share capital of the stocks. As all listed companies are taken as samples, its representativeness is very extensive, and it is released simultaneously with Shenzhen Stock Exchange, which is a necessary reference for investors and securities practitioners to judge the trend of stock price changes in Shenzhen Stock Exchange. A few years ago, because the stock trading in Shenzhen Stock Exchange was not as active as that in Shanghai Stock Exchange, now Shenzhen Stock Exchange has changed the way of compiling stock indexes, and adopted constituent stock indexes, of which only 40 stocks were selected and released in May of 1995.

At present, there are two stock indexes in Shenzhen Stock Exchange, one is the old Shenzhen Composite Index, and the other is the current constituent stock index. However, judging from the operation in recent years, the difference between the two indicators is not particularly obvious.