Who determines, and how, the composition of the S&P 500 index?
"The S&P 500 index is maintained by S&P Dow Jones Indices, a division of McGraw Hill Financial. Changes to the index are made periodically, as needed.  For Facebook, you'll find it mentioned in this December 11, 2013 press release (PDF).  Quote: New York, NY, December 11 , 2013 – S&P Dow Jones Indices will make the following changes to the S&P 100, S&P 500, MidCap 400   and S&P SmallCap 600 indices after the close of trading on Friday,   December 20: You can find out more about the S&P 500 index eligibility criteria from the S&P U.S. Indices methodology document (PDF).  See pages 5 and 6: Market Capitalization - [...] Liquidity - [...] Domicile - [...] Public Float - [...] Sector Classification - [...] Financial Viability - Usually measured as four consecutive quarters of positive as   reported earnings. [...] Treatment of IPOs - Initial public offerings should be seasoned for 6 to 12 months   before being considered for addition to an index. Eligible Securities - [...]   [...]   Changes to the U.S. indices other than the TMIX are made as needed,   with no annual or  semi-annual reconstitution. [...] LabCorp may have a smaller market cap than Facebook, but Facebook didn't meet all of the eligibility criteria – for instance, see the above note about ""Treatment of IPOs"" – until recently. Note also that ""Initial public offerings should be seasoned for 6 to 12 months"" implies somebody at S&P makes a decision as to the exact when. As such, I would say, no, there is no ""simple rule or formula"", just the methodology above as applied by the decision-makers at S&P." 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.
In general, the goal of an S&P 500 index fund is to replicate the performance of the S&P 500 Index.  To do this, the fund will buy the same stocks in the same proportions as the weighting of the Index. The S&P 500 Index is free-float capitalization weighted.  This means that the higher capitalization stocks (based on publicly traded shares only) are more heavily weighted and factor into the Index value more heavily than the smaller capitalization stocks, or the stocks that have a smaller publicly traded value.  For example, companies like Apple, ExxonMobil, and Microsoft have a much larger weight in the index value than smaller companies. Alternatively, there are some S&P index funds that are equal-weighted.  In these funds, the managers have chosen to purchase all 500 of the stocks in the index, but in equal proportions instead of the weighted proportions of the index.  These equal-weighted funds will not as closely match the index price as the traditionally weighted index funds.  Instead, they might do better or worse than the index, depending on how the individual stocks do. You'll need to look at the prospectus of the index funds you are interested in to see which approach the fund is taking. try over in /r/personalfinance  Economics is about understanding the economy and how it works. Investing is about taking your money and putting it somewhere useful. They're related; but what you want probably isn't economy-wide advice, but specific individual options.  FYI, they'll recommend you get into some index fund to start; one that just tracks a big index like the Dow Jones, Nasdaq, or S&amp;P 500. These help diversify your risk and tend to offer good returns. But, a lot depends on what your personal situation entails, so head on over there and read their FAQ. From Wikipedia -  To calculate the value of the S&P 500 Index, the sum of the adjusted   market capitalization of all 500 stocks is divided by a factor,   usually referred to as the Divisor. For example, if the total adjusted   market cap of the 500 component stocks is US$13 trillion and the   Divisor is set at 8.933 billion, then the S&P 500 Index value would be   1,455.28. From a strictly mathematical perspective, the divisor is not canceling out the units, and the S&P index is dollar denominated even though it's never quoted that way. A case in point is that the S&P is often said to have a P/E, and especially an E, the earnings attributed to one 'unit' of S&P. And if you buy a mutual fund sporting a low expense ratio, you can invest exactly that much money (the current S&P index value) and see the dividends accrue to your account, less the fee. Victor, Yes the drop in price does completely cancel the dividend at first. However, as others have noted, there are other forces working on the price as well. If dividends were pointless then the following scenario would be true: Let's assume, hypothetically, two identical stocks, only one of which pays a 2% annual dividend quarterly. At the end of the year we would expect the share price of the dividend stock to be 2% lower than the non-dividend stock.  And an equal investment in both stocks would yield exactly the same amount of money. So that is a hypothetical, and here is real market example: I compared, i.e. took the ratio of Vanguard's S&P 500 ETF (VOO) closing price to the S&P 500 Index closing price from sep 9, (2010-2014), after accounting for the VOO 2013 split. The VOO pays a quarterly dividend(about 2%/year), the S&P is an index, hence no dividend. The VOO share price, reduced each quarter by the dividend, still grew more than the S&P each year except 2012 to 2013, but looking at the entire 4yr period the VOO share price grew 80.3987% while S&P grew 80.083% (1/3 of 1% more for VOO). VOO does drop about 1/2% relative to S&P on every ex date, but obviously it makes it up. There are other forces working on VOO. VOO is trade-able, therefore subject to supply/demand pressures, while the S&P 500 is not. So for the VOO ETF the data does not indicate pointless dividends but instead implies dividends are free money. StockCharts.com supports this.  S&P500 for last 1244 days (9/8/2010) shows 90% growth http://stockcharts.com/freecharts/perf.php?%24SPX while VOO for last 1244 days shows 105% growth http://stockcharts.com/freecharts/perf.php?VOO Theoretically, it could be daily, but depending upon the number of companies in the index, it could be anywhere between daily or once a month or so. Apart from that, there is a periodic index review that happens once every quarter. The methodology for each index is also different, and you need to be aware of it (we had positions on literally hundreds of indices, and I knew the methodology of almost each of them).  If you have say, 2 billion dollars tracking a certain index, even a miniscule change in the composition would be substantial for you. But for certain others, you may just need to buy and sell $10k worth of stocks, and we would not even bother. &gt; So what’s the problem? When investors put their money in an index like the S&amp;P 500, they believe that they are just investing in “the market”, broadly. But now, these for-profit indices have made an active decision to exclude certain stocks on the basis of their voting structures.   The author doesn't seem to understand the difference between the companies creating the passive funds that track the indices and the companies creating the indices that are being tracked. Indices have always been subject to somewhat arbitrary rules for what is being included and how its value is calculated. So this article is completely missing the point. Generally S&P 500 will be used as the benchmark for US investors because it represents how's the US market performs as a whole. If you've outperformed the S&P 500 during the last couple years, great. However, at the end of day, you would want to look at the total growth percent that your portfolio has achieved, as compared with that of S&P 500.  Anyway, your portfolio might actually ride along with the bull market during the 2009-2010 period (more-so for the small caps). I can see your point.  There are more investors than investment banks, so the power of each investment bank is substantially more than each individual investor.  It would take a lot of coordinated effort on the part of investors to alter the balance of power.  And to an extent, a new or existing and improved ratings agency would be a proxy war between investors and investment banks, even though the direct competition would be with other ratings agencies.  At the same time, ratings agencies as an industry have never had less credibility, nor have the investment banks for that matter.  I have to believe there is a realistic way to exploit that reality.