At present, there are many references to domestic US stock index and fragrant stock index. The US stock indexes include Dow Jones Industrial Average, Nasdaq Composite Index and Standard & Poor's 500 Index, and the fragrant stock index is Hang Seng Index.
：
Stock market index is a reference index compiled by stock exchanges or financial services institutions to reflect changes in the stock market.
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.
Due to the complexity and variety of stock index calculation, people often select several 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.
Calculation method
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.
Exponential calculation
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.