Why buy SPY when there is S&P500?
The S&P500 is an index, not an investment by itself.  The index lists a large number of stocks, and the value of the index is the price of all the stocks added together. If you want to make an investment that tracks the S&P500, you could buy some shares of each stock in the index, in the same proportions as the index.  This, however, is impractical for just about everyone. Index mutual funds provide an easy way to make this investment.  SPY is an ETF (exchange-traded mutual fund) that does the same thing. An index CFD (contract for difference) is not the same as an index mutual fund.  There are a number of differences between investing in a security fund and investing in a CFD, and CFDs are not available everywhere.
As someone fairly new to finance and investing in their 30s, the market is doing too well right now for me to use someone else to tell me how to invest the Sp500 alone is doing so well it is almost a can't miss. I am smart enough to know right now that it is easy and the real value if a financial planner comes when the market is going down. Which is impossible to predict. 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'm confused. Are you asking why or telling us that you're bullish? Yes the stock will go up for a merger at a premium, but buying in now only gives you ~0.5% gain if it closes at $21.50. They won't trade over 21.50 unless a competing bid comes in or the bid is increased. "Index funds are well-known to give the best long-term investment. Not exactly. Indexes give the best long term performance when compared to actively managing investments directly in the underlying stocks. That is, if you compare an S&P500 index to trying to pick stocks that are part of it, you're more likely to succeed with blindly following the index than trying to actively beat it. That said, no-one promises that investing in S&P500 is better than investing in DJIA, for example. These are two different indexes tracking different stocks and areas. So when advisers say ""diversify"" they don't mean it that you should diversify between different stocks that build up the S&P500 index. They mean that you should diversify your investments in different areas. Some in S&P500, some in DJIA, some in international indexes, some in bond indexes, etc. Still, investing in various indexes will likely yield better results than actively managing the investments trying to beat those indexes, but you should not invest in only one, and that is the meaning of diversification. In the comments you asked ""why diversify at all?"", and that is entirely a different question from your original ""what diversification is?"". You diversify to reduce the risk of loss from one side, and widen the net for gains from another. The thing is that any single investment can eventually fail, regardless of how it performed before. You can see that the S&P500 index lost 50% of its value twice within ten years, whereas before it was doubling itself every several years. Many people who were only invested in that index (or what's underlying to it) lost a lot of money. But consider you've diversified, and in the last 20 years you've invested in a blend of indexes that include the S&P500, but also other investments like S&P BSE SENSEX mentioned by Victor below. You would reduce your risk of loss on the American market by increasing your gains on the Indian market. Add to the mix soaring Chinese Real Estate market during the time of the collapse of the US real-estate, gains on the dollar losing its value by investing in other currencies (Canadian dollar, for example), etc. There are many risks, and by diversifying you mitigate them, and also have a chance to create other potential gains. Now, another question is why invest in indexes. That has been answered before on this site. It is my opinion that some methods of investing are just gambling by trying to catch the wave and they will almost always fail, and rarely will individual stock picking beat the market. Of course, after the fact its easy to be smart and pick the winning stocks. But the problem is to be able to predict those charts ahead of time." 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 :) "If there's indeed no reason to trust GS, i.e. those are just guides   then the question is: Why do investors seem to care? Because there's a reason to trust. You're just reading the bottom line - the target price range. More involved investors read the whole report, including the description of the current situation, the premises for the analysis, the expectations on the firm's performance and what these expectations are based on, the analysis of how the various scenarios might affect the valuation, and the evaluation of chances of these scenarios to occur. You don't have to trust everything and expect it to be 100% correct, analysts are not prophets. But you do have an option of reading their reports and critically analyzing their conclusions. What you suspect GS of doing (""I tend to believe those guys just want themselves a cheap buy price a few days before Q2 earnings release"") is a criminal offence." "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." One reason it matters whether or not you're beating the S&P 500 (or the Wilshire 5000, or whatever benchmark you choose to use) is to determine whether or not you'd be better off investing in an index fund (or some other investment vehicle) instead of pursuing whatever your current investment strategy happens to be.  Even if your investment strategy makes money, earning what the S&P 500 has averaged over multiple decades (around 10%) with an index fund means a lot more money than a 5% return with an actively managed portfolio (especially when you consider factors like compound interest and inflation). I use the S&P 500 as one of my criteria for judging how well (or poorly) my financial adviser is doing for me. If his recommendations (or trading activity on my behalf, if authorized) are inferior to the S&P 500, for too long, then I have a basis to discontinue the relationship. Check out this Wikipedia entry on stock market indices. There are legitimate criticisms, but on the whole I think they are useful. As an aside, the reason I point to index funds specifically is that they are the one of the lowest-cost, fire-and-forget investment strategies around.  If you compare the return of the S&P 500 index over multiple decades with most actively managed mutual funds, the S&P 500 index comes out ahead. 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. Today SPY (The S&P ETF) trades at $128. The option to buy at $140 (this is a Jan '13 call) trades for $5.  I buy the call, for $500 as they trade in 100 lots.  The S&P skyrockets to 1500 and SPY to $150. The call trades for $11, as it still has a month or two before expiring, so I sell it, and get $1100. The S&P rose 17%, but I doubled my money. If it 'only' rose 9%, to less than $140, I'd lose my investment. No, I don't need to buy the SPY I can sell the call any time before expiration. In fact, most options are not exercised, they are sold between purchase and expiration date. As Ross says, SPX is the index itself. This carries no overheads. It is defined as a capitalization-weighted mixture of the stocks of (about) 500 companies. SPY is an index fund that tries to match the performance of SPX. As an index fund it has several differences from the index: 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. With the disclaimer that I am not a technician, I'd answer yes, it does. SPY (for clarification, an ETF that reflects the S&P 500 index) has dividends, and earnings, therefore a P/E and dividend yield. It would follow that the tools technicians use, such as moving averages, support and resistance levels also apply.  Keep in mind, each and every year, one can take the S&P stocks and break them up, into quintiles or deciles based on return and show that not all stock move in unison. You can break up by industry as well which is what the SPDRs aim to do, and observe the movement of those sub-groups.  But, no, not all the stocks will perform the way the index is predicted to.  (Note - If a technician wishes to correct any key points here, you are welcome to add a note, hopefully, my answer was not biased) Why not figure out the % composition   of the index and invest in the   participating securities directly? This isn't really practical.   Two indices I use follow the Russell 2000 and the S&P 500 Those two indices represent 2500 stocks. A $4 brokerage commission per trade would mean that it would cost me $10,000 in transaction fees to buy a position in 2500 stocks. Not to mention, I don't want to track 2500 investments. Index funds provide inexpensive diversity. Here's the 2009-2014 return of the S&P 500 (SPY) vs. Vanguard FTSE ex-US (VEU) (higher returns bolded) Another argument for them is their low correlation to U.S stocks.   Looking at history however, I don't see it. Most times U.S stocks have   done badly, foreign stocks have also done badly. Looking at the last 6 years (and current YTD), 1 in 3 years have international stocks doing better.    I invest a portion of my investments in international because they aren't well correlated.