The Dow Jones Industrial Average (DJIA), or simply the Dow, is a stock market index that measures the stock performance of 30 large companies listed on stock exchanges in the United States. Although it is one of the most commonly followed equity indices, since it only includes 30 companies and is not weighted by market capitalization and is not a weighted arithmetic mean, many consider the Dow to not be a good representation of the U.S. stock market and consider the S&P 500 Index, which also includes the 30 components of the Dow, to be a better representation of the U.S. stock market.