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.
Now, if I'm not mistaken, tracking a value-weighted index is extremely easy - just buy the shares in the exact amount they are in the index and wait. Yes in theory. In practise this is difficult. Most funds that track S&P do it on sample basis. This is to maintain the fund size. Although I don't have / know the exact number ... if one wants to replicate the 500 stocks in the same %, one would need close to billion in fund size. As funds are not this large, there are various strategies adopted, including sampling of companies [i.e. don't buy all]; select a set of companies that mimic the S&P behaviour, etc. All these strategies result in tracking errors. There are algorithms to reduce this. The only time you would need to rebalance your holdings is when there is a change in the index, i.e. a company is dropped and a new one is added, right? So essentially rebalance is done to; If so, why do passive ETFs require frequent rebalancing and generally lose to their benchmark index? lets take an Index with just 3 companies, with below price. The total Market cap is 1000  The Minimum required to mimic this index is 200 or Multiples of 200. If so you are fine.    More Often, funds can't be this large. For example approx 100 funds track the S&P Index. Together they hold around 8-10% of Market Cap. Few large funds like Vangaurd, etc may hold around 2%. But most of the 100+ S&P funds hold something in 0.1 to 0.5 range. So lets say a fund only has 100. To maintain same proportion it has to buy shares in fraction. But it can only buy shares in whole numbers. This would then force the fund manager to allocate out of proportion, some may remain cash, etc. As you can see below illustrative, there is a tracking error. The fund is not truly able to mimic the index.  Now lets say after 1st April, the share price moved, now this would mean more tracking error if no action is taken [block 2] ... and less tracking error if one share of company B is sold and one share of company C is purchased.  Again the above is a very simplified view. Tracking error computation is involved mathematics.  Now that we have the basic concepts, more often funds tracking S&P; Thus they need to rebalance. ETFs have caused many if not most stocks on the SP500 to become correlated.  I think at some point in the last couple of years, 90% of the SP500 were correlated to the index itself.  So you're going to see a lot of movement together of most stocks. "The S&P 500 is an index. This refers to a specific collection of securities which is held in perfect proportion. The dollar value of an index is scaled arbitrarily and is based off of an arbitrary starting price. (Side note: this is why an index never has a ""split""). Lets look at what assumptions are included in the pricing of an index: All securities are held in perfect proportion. This means that if you invest $100 in the index you will receive 0.2746 shares of IBM, 0.000478 shares of General Motors, etc. Also, if a security is added/dropped from the list, you are immediately rebalancing the remaining money. Zero commissions are charged. When the index is calculated, they are using the current price (last trade) of the underlying securities, they are not actually purchasing them. Therefore it assumes that securities may be purchased without commission or other liquidity costs. Also closely related is the following. The current price has full liquidity. If the last quoted price is $20 for a security, the index assumes that you can purchase an arbitrary amount of the security at that price with a counterparty that is willing to trade. Dividends are distributed immediately. If you own 500 equities, and most distributed dividends quarterly, this means you will receive on average 4 dividends per day. Management is free. All equities can be purchased with zero research and administrative costs. There is no gains tax. Trading required by the assumptions above would change your holdings constantly and you are exempt from short-term or long-term capital gains taxes. Each one of these assumptions is, of course, invalid. And the fund which endeavors to track the index must make several decisions in how to closely track the index while avoiding the problems (costs) caused by the assumptions. These are shortcuts or ""approximations"". Each shortcut leads to performance which does not exactly match the index. Management fees. Fees are charged to the investor as load, annual fees and/or redemptions. Securities are purchased at real prices. If Facebook were removed from the S&P 500 overnight tonight, the fund would sell its shares at the price buyers are bidding the next market day at 09:30. This could be significantly different than the price today, which the index records. Securities are purchased in blocks. Rather than buying 0.000478 shares of General Motors each time someone invests a dollar, they wait for a few people and then buy a full share or a round lot. Securities are substituted. With lots of analysis, it may be determined that two stocks move in tandem. The fund may purchase two shares of General Motors rather than one of General Motors and Ford. This halves transaction costs. Debt is used. As part of substitution, equities may be replaced by options. Option pricing shows that ownership of options is equivalent to holding an amount of debt. Other forms of leverage may also be employed to achieve desired market exposure. See also: beta.  Dividends are bundled. VFINX, the largest S&P 500 tracking fund, pays dividends quarterly rather than immediately as earned. The dividend money which is not paid to you is either deployed to buy other securities or put into a sinking fund for payment. There are many reasons why you can't get the actual performance quoted in an index. And for other more exotic indices, like VIX the volatility index, even more so. The best you can do is work with someone that has a good reputation and measure their performance." 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. It's either a broad benchmark sp500, msci world, lehman agg, and or a cash index. Most will not use a specific benchmark.  While the broad benchmark may not be applicable from my experience its usually there as a proxy for the overall market. Multiple overlapping indices exist covering various investment universes.  Almost all of the widely followed indices were originally created by Lehman Brothers and are now maintained by Barclays.  The broadest U.S. dollar based bond index is known as the Universal.  The Aggregate (often abbreviated Agg), which is historically the most popular index, more or less includes all bonds in the Universal rated investment grade.  The direct analog to the S&P 500 would be the U.S. Corporate Investment Grade index, which is tracked by the ETF LQD, and contains exactly what it sounds like. Citigroup (formerly Salomon Brothers) also has a competitor index to the Aggregate known as Broad Investment Grade (BIG), and Merrill Lynch (now Bank of America) has the Domestic Master. Multiple other indices also exist covering other bond markets, such as international (non-USD) bonds, tax-exempts (municipal bonds), securitized products, floating rate, etc. "Split your contributions evenly across the funds on that list with the word ""core"" or ""S&P"" in the name.  Maybe add ""International Large Cap Index"".  Leave it & rebalance occasionally.  Read a book on Modern Portfolio Theory sometime in the next 5 years." "The Dow Jones Industrial Average (DJIA) is a Price-weighted index.  That means that the index is calculated by adding up the prices of the constituent stocks and dividing by a constant, the ""Dow divisor"".  (The value of the Dow divisor is adjusted from time to time to maintain continuity when there are splits or changes in the roster.)  This has the curious effect of giving a member of the index influence proportional to its share price.  That is, if a stock costing $100 per share goes up by 1%, that will change the index by 10 times as much as if a stock costing $10 per share goes up by the same 1%. Now look at the price of Google.  It's currently trading at just a whisker under $700 per share.  Most of the other stocks in the index trade somewhere between $30 and $150, so if Google were included in the index it would contribute between 5 and 20 times the weight of any other stock in the index.  That means that relatively small blips in Google's price would completely dominate the index on any given day.  Until June of 2014, Apple was in the same boat, with its stock trading at about $700 per share.  At that time, Apple split its stock 7:1, and after that its stock price was a little under $100 per share.  So, post-split Apple might be a candidate to be included in the Dow the next time they change up the components of the index.  Since the Dow is fixed at 30 stocks, and since they try to keep a balance between different sectors, this probably wouldn't happen until they drop another technology company from the lineup for some reason.  (Correction: Apple is in the DJIA and has been for a little over a year now.  Mea culpa.) The Dow's price-weighting is unusual as stock indices go.  Most indices are weighted by market capitalization.  That means the influence of a single company is proportional to its total value.  This causes large companies like Apple to have a lot of influence on those indices, but since market capitalization isn't as arbitrary as stock price, most people see that as ok.  Also, notice that I said ""company"" and not ""stock"".  When a company has multiple classes of share (as Google does), market-cap-weighted indices include all of the share classes, while the Dow has no provision for such situations, which is another, albeit less important, reason why Google isn't in the Dow.  (Keep this in mind the next time someone offers you a bar bet on how many stocks are in the S&P 500.  The answer is (currently) 505!) Finally, you might be wondering why the Dow uses such an odd weighting in its calculations.  The answer is that the Dow averages go back to 1896, when Charles Dow used to calculate the averages by hand.  If your only tools are a pencil and paper, then a price-weighted index with only 30 stocks in it is a lot easier to calculate than a market-cap-weighted index with hundreds of constituents. About the Dow Jones Averages. Dow constituents and prices Apple's stock price chart. The split in 2014 is marked.  (Note that prices before the split are retroactively adjusted to show a continuous curve.)" If you have access, factset and bloomberg have this.  However, these aren't standardized due to non-existent reporting regulations, therefore each company may choose to categorize regions differently.  This makes it difficult to work with a large universe, and you'll probably end up doing a large portion manually anyways. I hate to point to Wikipedia as an answer, but it does describe exactly what you are looking for... The S&P 500 is a free-float   capitalization-weighted index   published since 1957 of the prices of   500 large-cap common stocks actively   traded in the United States. The   stocks included in the S&P 500 are   those of large publicly held companies   that trade on either of the two   largest American stock market   exchanges; the New York Stock Exchange   and the NASDAQ. The components of the S&P 500 are   selected by committee... The committee   selects the companies in the S&P 500   so they are representative of the   industries in the United States   economy. In addition, companies that   do not trade publicly (such as those   that are privately or mutually held)   and stocks that do not have sufficient   liquidity are not in the index. The S&P is a capitalization weighted index.  If a stock price goes up, then it comprises more of the total index.  If a stock goes down, it comprises less, and if it goes down too much, the committee will likely replace it. So to answer your question, if one stock were to suddenly skyrocket, nothing would happen beyond the fact that the index was now worth more and that particular stock would now make up a larger percentage of the S&P 500 index. Is it POSSIBLE? Of course. I don't even need to do any research to prove that. Just some mathematical reasoning: Take the S&P 500. Find the performance of each stock in that list over whatever time period you want to use for your experiment. Now select some number of the best-performing stocks from the list -- any number less than 500. By definition, the X best must be better than or equal to the average. Assuming all the stocks on the S&P did not have EXACTLY the same performance, these 10 must be better than average. You now have a diversified portfolio that performed better than the S&P 500 index fund. Of course as they always say in a prospectus, past performance is not a guarantee of future performance.  It's certainly possible to do. The question is, if YOU selected the stocks making up a diversified portfolio, would your selections do better than an index fund? What makes the S&P 500 Index funds have low expenses ratios is that the amount of money spent by the mutual fund company on research is Zero. Standard and Poors does the research, the fund companies piggy back on that research.  Another big factor in keeping expenses low is the fact the companies that makeup the index don't change very often. If the fund frequently changes the makeup of the investments not only can that trigger tax considerations but there are costs associated with all those transactions. The question is: do the other algorithms overcome the additional costs due to higher expenses and taxes. As I write this, the NASDAQ Composite is at 2790.00, down 6.14 points from yesterday. To calculate the percentage, you take 6.14 and divide by yesterday's close of 2796.14 to yield 0.22%. In your example, if SPY drops from 133.68 to 133.32, you use the difference of -0.36 and divide by the original, i.e. -0.36/133.68 = -0.27%. SPY is an ETF which you can invest in that tracks the S&P 500 index. Ideally, the index would have dropped the same percentage as SPY, but the points would be different (~10x higher). To answer your question about how one qualifies a point, it completely depends on the index being discussed. For example, the S&P 500 is a market-capitalization weighted index of the common stock of 500 large-cap US public companies. It is as if you owned every share of each of the 500 companies, then divide by some large constant to create a number that's easily understood mentally (i.e. 1330). The NASDAQ Composite used the same methodology but includes practically all stocks listed on the NASDAQ. Meanwhile, the Dow Jones Industrial Average is a price-weighted index of 30 large-cap companies. It's final value is modified using a divisor known as the Dow Divisor, which accounts for stock splits and similar events that have occurred since a stock has joined the index. Thus, points when referring to an index do not typically represent dollars. Rather, they serve as a quantitative measure of how the market is doing based on the performance of the index constituents. ETFs like SPY add a layer of abstraction by creating an investible vehicle that ideally tracks the value of the underlying index directly. Finally, neither price nor index value is related to volume. Volume is a raw measurement of the total number of shares traded for a given stock or the aggregate for a given exchange. Hope this helps! The equation you show is correct, you've simply pointed out that you understand that you buy at the 'ask' price, and later sell at the 'bid.' There is no bid/ask on the S&P, as you can't trade it directly.  You have a few alternatives, however - you can trade SPY, the (most well known) S&P ETF whose price reflects 1/10 the value or VOO (Vanguard's offering) as well as others. Each of these ETFs gives you a bid/ask during market hours. They trade like a stock, have shares that are reasonably priced, and are optionable.  To trade the index itself, you need to trade the futures. S&P 500 Futures and Options is the CME Group's brief info guide on standard and mini contracts.  Welcome to SE. I wouldn't use it to take leverage unless you don't mind loosing your entire investment (this is a possibility as shares are already quite volatile). However, you don't have to take leverage and still trade CFDs. Benefits of doing so: Disadvantages: