What is the “point” (purpose) of the S&P 500?
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.
"As Dheer pointed out, the top ten mega-cap corporations account for a huge part (20%) of your ""S&P 500"" portfolio when weighted proportionally. This is one of the reasons why I have personally avoided the index-fund/etf craze -- I don't really need another mechanism to buy ExxonMobil, IBM and Wal-Mart on my behalf. I like the equal-weight concept -- if I'm investing in a broad sector (Large Cap companies), I want diversification across the entire sector and avoid concentration. The downside to this approach is that there will be more portfolio turnover (and expense), since you're holding more shares of the lower tranches of the index where companies are more apt to churn. (ie. #500 on the index gets replaced by an up and comer). So you're likely to have a higher expense ratio, which matters to many folks." The compound annual growth rate of the S&P 500 over the last 20 years is in excess of 7% annually. http://www.moneychimp.com/features/market_cagr.htm Several index funds mirror the S&P 500 such as, but not limited to SPDR S&P 500 ETF Trust. An annual growth rate of 7% on a $5,000,000 portfolio implies gains of $350,000 per year, every year investing passively. Most of us can live reasonably well on $350,000 per year! I will argue that the chances of all 500 companies in the S&P 500 going bankrupt or nearly so at once is slight and less likely than the same for Google. The S&P 500 represents a broadly diversified basket of stocks.  Silver is a single metal.  If all else is equal, more diversification means less volatility.  A better comparison would be the S&P 500 vs. a commodities index, or silver vs. some individual stock. "There is no simple answer to that, because no one knows exactly what the probability distribution of S&P 500 returns is. Here is a sketch of one possible way to proceed. Don't forget step 4!  The problem is that the stock market is full of surprises, so this kind of ""backtesting"" can only reliably tell you about what already happened, not what will happen in the future.  People argue about how much you can learn from this kind of analysis.  However, it is at the least a clearly defined and objective process.  I wouldn't advise investing your whole nest egg in anything based just on this, but I do think that it is relevant information." "TL;DR: Because stocks represent added value from corporate profits, and not the price the goods themselves are sold at. This is actually a very complicated subject.  But here's the simplest answer I can come up with.  Stocks are a commodity, just like milk, eggs, and bread.  The government only tracks certain commodities (consumables) as part of the Consumer Price Index (CPI).  These are generally commodities that the typical person will consume on a daily or weekly basis, or need to survive (food, rent, etc.).  These are present values. Stock prices, on the other hand, represent an educated guess (or bet) on a company's future performance.  If Apple has historically performed well, and analysts expect it to continue to perform, then investors will pay more for a stock that they feel will continue pay good dividends in the future.  Compound this with the fact that there is usually limited a supply of stock for a particular company (unless they issue more stock). If we go back to Apple as an example, they can raise their price they charge on an iPhone from $400 to $450 over the course of say a couple years.  Some of this may be due to higher wage costs, but efficiencies in the marketplace actually tend to drive down costs to produce goods, so they will probably actually turn a higher profit by raising their price, even if they have to pay higher wages (or possibly even if they don't raise their price!).  This, in economics, is termed value added. Finally, @Hart is absolutely correct in his comment about the stocks in the S&P 500 not being static.  Additionally, the S&P 500 is a hand picked set of ""winners"", if you will.  These are not run-of-the-mill penny stocks for companies that will be out of business in a week.  These are companies that Standard & Poor's Financial Services LLC thinks will perform well." IESC has a one-time, non-repeatable event in its operating income stream.  It magnifies operating income by about a factor of five.  It impacts both the numerator and the denominator.  Without knowing exactly how the adjustments are made it would take too much work for me to calculate it exactly, but I did get close to their number using a relatively crude adjustment rule. Basically, Yahoo is excluding one-time events from its definitions since, although they are classified as operating events, they distort the financial record.  I teach securities analysis and have done it as a profession.  If I had to choose between Yahoo and Marketwatch, at least for this security, I would clearly choose Yahoo. "While it's definitely possible (and likely?) that a diversified portfolio generates higher returns than the S&P 500, that's not the main reason why you diversify. Diversification reduces risk.  Modern portfolio theory suggests that you should maximize return while reducing risk, instead of blindly chasing the highest returns. Think about it this way--say the average return is 11% for large cap US stocks (the S&P 500), and it's 10% for a diversified portfolio (say, 6-8 asset classes). The large cap only portfolio has a 10% chance of losing 30% in a given year, while the diversified portfolio has a 1% chance of losing 30% in a year. For the vast majority of investors, it's worth the 1% annual gap in expected return to greatly reduce their risk exposure. Of course, I just made those numbers up. Read what finance professors have written for the ""data and proof"". But modern portfolio theory is believed by a lot of investors and other finance experts. There are a ton of studies (and therefore data) on MPT--including many that contradict it." There are more companies in the S&amp;P500 that are tech enabled services companies, and a few are software as a service (salesforce, cerner, etc.). As a result profit margins used here have expanded. If wages increase, margins should shrink but there is likely going to be growing revenue as we still have a huge output gap because of all the unemployed people who would have income. Not sure there is a mean to regress to "I am guessing that when you say ""FRENCH40"" and ""GERMAN30"" you are referring to the main French and German stock market indices.  The main French index is the CAC-40 with its 40 constituent companies. The main German index is the DAX, which has 30 constituents.  The US30 is presumably the Dow Jones Index which also has 30 constituents. These are stock market indices that are used to measure the value of a basket of shares (the index constituents).  As the value of the constituents change, so does the value of the index. There are various financial instruments that allow investors to profit from movements in these indices.  It is those people who invest in these instruments that profit from price movements.  The constituent companies receive no direct benefit or profit from investor trading in these instruments, nor does the government." "Doing your homework means to perform what's more accurately called ""fundamental analysis"". According to proponents of fundamental analysis (FA), it is possible to accurately determine how much a stock should trade for and then buy or sell the stock based on whether it trades above or below this target price. This target price is based on the discounted anticipated future earnings of your stock, so ""doing your homework"" means that you figure out how much future earnings you can expect from the stock and then figuring out at what rate you want to discount those future earnings (Are 1000 dollars that you'll earn next year worth $800 today or $900 or only $500? That depends on the overall economic and political climate...) So does this make any sense? Depends. I'm aware that there are a lot of anecdotes of people researching a stock, buying that stock and doing well with that stock. But poor decisions can at times lead to good outcomes... EDIT: Due to some criticism, I want to expand on a few points. So, is homework completely for naught? No!" My level of analysis is not quite that advanced. Can you share what that would show and why that particular measure is the one to use?  I've run regression on prices between the two. VIX prices have no correlation to the s&amp;p500 prices. Shouldn't true volatility result in the prices (more people putting options on the VIX during the bad times and driving that price up) correlate to the selloff that occurs within the S&amp;P500 during recessions and other events that would cause significant or minor volatility? My r2 showed no significance within a measurement of regression within Excel.  But, *gasp* I could be wrong, but would love to learn more about better ways of measurement :) You are correct that over a short term there is no guarantee that one index will out perform another index. Every index goes through periods of feat and famine. That uis why the advice is to diversify your investments. Every index does have some small amount of management. For the parent index (the S&P 500 in this case) there is a process to divide all 500 stocks into growth and value, pure growth and pure value. This rebalancing of the 500 stocks occurs once a year. Rebalancing The S&P Style indices are rebalanced once a year in December. The   December rebalancing helps set the broad universe and benchmark for   active managers on an annual cycle consistent with active manager   performance evaluation cycles. The rebalancing date is the third   Friday of December, which coincides with the December quarterly share   changes for the S&P Composite 1500.  Style Scores,   market-capitalization weights, growth and value midpoint averages, and   the Pure Weight Factors (PWFs), where applicable across the various   Style indices, are reset only once a year at the December rebalancing. Other changes to the U.S. Style indices are made on an as-needed   basis, following the guidelines of the parent index. Changes in   response to corporate actions and market developments can be made at   any time. Constituent changes are typically announced for the parent   index two-to-five days before they are scheduled to be implemented. Please refer to the S&P U.S. Indices Methodology document for   information on standard index maintenance for the S&P 500, the S&P   MidCap 400,the S&P SmallCap 600 and all related indices. As to which is better: 500, growth,value or growth and value? That depends on what you the investor is trying to do. "I think that ""memoryless"" in this context of a given stock's performance is not a term of art. IMO, it's an anecdotal concept or cliche used to make a point about holding a stock. Sometimes people get stuck... they buy a stock or fund at 50, it goes down to 30, then hold onto it so they can ""get back to even"". By holding the loser stock for emotional reasons, the person potentially misses out on gains elsewhere." Many of the major indices retreated   today because of this news. Why? How   do the rising budget deficits and debt   relate to the stock markets? It does seem strange that there is a correlation between government debt and the stock market.  But I could see many reasons for the reaction.  The downgrade by S&P may make it more expensive for the government to borrow money (i.e. higher interest rates).  This means it becomes more expensive for the government to borrow money and the government will probably need to raise taxes to cover the cost of borrowing.  Rising taxes are not good for business.  Also, many banks in the US hold US government debt.  Rising yields will push down the value of their holdings which in turn will reduce the value of US debt on the businesses' balance sheets.  This weakens the banks' balance sheets.  They may even start to unload US bonds. Why is there such a large emphasis on   the S&P rating? I don't know.  I think they have proven they are practically useless.  That's just my opinion.  Many, though, still think they are a credible ratings agency. What happens when the debt ceiling is   reached? Theoretically the government has to stop borrowing money once the debt ceiling is reached.  If this occurs and the government does not raise the debt ceiling then the government faces three choices: Cost.  If an investor wanted to diversify his portfolio by investing in the companies that make up the S&P 500, the per-share and commission costs to individually place trades for each and every one of those companies would be prohibitive. I can buy one share of an exchange-traded fund that tracks the S&P 500 for less than the purchase price of a single share in some of the companies that make up the index.