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Who determines, and how, the composition of the S&P 500 index?
S & P's site has a methodology link that contains the following which may be of use: Market Capitalization. Unadjusted market capitalization of US$ 4.6   billion or more for  the S&P 500, US$ 1.2 billion to US$ 5.1 billion   for the S&P MidCap 400, and US$ 350  million to US$ 1.6 billion for   the S&P SmallCap 600. The market cap of a potential  addition to an   index is looked at in the context of its short- and medium-term   historical  trends, as well as those of its industry. These ranges are   reviewed from time to time to  assure consistency with market   conditions.  Liquidity. Adequate liquidity and reasonable price – the   ratio of annual dollar value  traded to float adjusted market   capitalization should be 1.00 or greater, and the company  should   trade a minimum of 250,000 shares in each of the six months leading up   to the  evaluation date.  Domicile. U.S. companies. For index purposes,   a U.S. company has the following  characteristics:  The final determination of domicile eligibility is made by the U.S.   Index Committee.