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.
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.