Indices measure statistical changes in a portfolio of stocks that represent a portion of the overall market. It then allows investors to focus the performance of major groupings of stocks. Charles Dow created the first known index in 1896, it contained 12 of the largest public companies in the U.S. Today, the Dow Jones Industrial Average (DJIA) contains 30 of the largest and most influential companies in the U.S. Other popular and well-known indices include the S&P and the NASDAQ