what is the most widely cited u s stock index 
the dow jones industrial average is the oldest u s stock index as well as the most frequently cited one however the s p 500 represents a larger cross section of the economy 10the bottom linemarket indexes are hypothetical portfolios of investment holdings that investors use as an indicator of market movement there are many different types of market indexes market indexes are also used to create index funds allowing investors to buy a basket of securities rather than picking individual stocks 