What Does the S&P 500 Index Measure and How Is It Calculated?

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The S&P 500 measures the value of the stocks of the 500 largest corporations by market capitalization listed on the New York Stock Exchange or Nasdaq Composite. The intention of Standard & Poor's is to have a price that provides a quick look at the stock market and economy. Indeed, the S&P 500 index is the most popular measure used by financial media and professionals, while the mainstream media and the general public might be more familiar with the Dow Jones Industrial Average.