The S&P 500 is a stock index that basket includes the top 500 selected US stock companies. The list is owned and compiled by Standard & Poor’s. The index has been published since March 4, 1957. 1941-1943 years were taken as the base period for the calculation, the base value is 10.
All S&P 500 companies are listed on major US stock exchanges such as the New York Stock Exchange and NASDAQ. The S&P 500 index value reflects their total capitalization (since 2006, adjusted for free-float). Since the weight of each company in the index is proportional to its capitalization, the index is weighted by capitalization. The S&P 500 competes in popularity with the Dow Jones Industrial Average and is deservedly called the barometer of the American economy.
The list of S&P 500 companies is not the same as the list of the largest US companies, as it does not include privately owned companies and companies with insufficient liquidity, i.e. do not reach the minimum trading volume of 250,000 shares in the month prior to valuation. In addition, when compiling the list, the authors try to fully represent the various sectors of the American economy.