Program Trading Accounts For About 45% Of Trading Volume On The NYSE

Note that it involves the S & P 500.

"Program trading is a generic term used to describe a type of trading in securities, usually consisting of stocks traded on the New York Stock Exchange and their corresponding options traded on the Chicago Board Options Exchange and/or the American Stock Exchange; and, the Standard & Poor's 500 Index commodity contract traded on the Chicago Mercantile Exchange. The trading of these items is based purely on their price in relation to each other on a predetermined basis; and not, on any fundamental reason such as an individual company's earnings, dividends, or growth prospects; or, on any overall economic reasons such as interest rate movements, currency fluctuations, or governmental or political actions. There are different types of program trading that we will describe later along with how you can benefit from the different types. According to the New York Stock Exchange, program trading accounts for about 45% of the trading volume on that exchange every day. "

http://www.programtrading.com/faq.htm