Does a bid and ask price exist for indices like the S&P500?
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. You can trade an index by using a Contract For Difference, or CFD. Various brokers offer this method and the spreads are quite low. They tend to widen outside of market hours, and not all brokers offer the same spreads. I would look for a broker that offers the lowest spread on the index you are interested in. You should also do your due diligence and check they are regulated by the relevant authority  pertaining to their territory, eg FSA for uk Bid and ask prices of stocks change not just daily, but continuously.  They are, as the names suggest, what price people are asking for to be willing to sell their stock, and how much people are bidding to be willing to buy it at that moment. Your equation is accurate in theory, but doesn't actually apply.  The bid and ask prices are indicators of the value of the stock, but the only think you care about as a trader are what you actually pay and sell it for.  So regardless of the bid/ask the equation is: Since you cannot buy an index directly (index, like indicator) it doesn't make sense to discuss how much people are bidding or asking for it.  Like JoeTaxpayer said, you can buy (and therefore bid/ask) for ETFs and funds that attempt to track the value of the S&P 500.
I've never heard of such a thing, but seems like if such a product existed it would be easily manipulated by the big trading firms - simply bet that trading volume will go up, then furiously buy and sell shares yourself to artificially drive up the volume. The fact that it would be so easily manipulated makes me think that no such product exists, but I could be wrong. Neither site offers index futures or options pricing.  Your best best is likely to get the quote from a broker who supports trading those vehicles. Free sites usually limit themselves to stocks and sometimes to options chains -- the exception is Reuters where just about any security for which you have the reuters formatted trading symbol can be quoted. "In practice, most (maybe all) stock indices are constructed by taking a weighted average of stock prices denominated in a single currency, and so the index implicitly does have that currency - as you suggest, US dollars for the S&P 500. In principle you can buy one ""unit"" of the S&P 500 for $2,132.98 or whatever by buying an appropriate quantity of each of its constituent stocks. Also, in a more realistic scenario where you buy an index via a tracker fund, you would typically need to buy using the underlying currency of the index and your returns will be relative to that currency - if the index goes up by 10%, your original investment in dollars is up by 10%." 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. "At the bottom of Yahoo! Finance's S & P 500 quote Quotes are real-time for NASDAQ, NYSE, and NYSE MKT. See also delay   times for other exchanges. All information provided ""as is"" for   informational purposes only, not intended for trading purposes or   advice. Neither Yahoo! nor any of independent providers is liable for   any informational errors, incompleteness, or delays, or for any   actions taken in reliance on information contained herein. By   accessing the Yahoo! site, you agree not to redistribute the   information found therein. Fundamental company data provided by Capital IQ. Historical chart data   and daily updates provided by Commodity Systems, Inc. (CSI).   International historical chart data, daily updates, fund summary, fund   performance, dividend data and Morningstar Index data provided by   Morningstar, Inc. Orderbook quotes are provided by BATS Exchange. US   Financials data provided by Edgar Online and all other Financials   provided by Capital IQ. International historical chart data, daily   updates, fundAnalyst estimates data provided by Thomson Financial   Network. All data povided by Thomson Financial Network is based solely   upon research information provided by third party analysts. Yahoo! has   not reviewed, and in no way endorses the validity of such data. Yahoo!   and ThomsonFN shall not be liable for any actions taken in reliance   thereon. Thus, yes there is a DB being accessed that there is likely an agreement between Yahoo! and the providers." You'd have to buy that information. Quoting from this page, Commercial Historical Data Higher resolution and more complete datasets are generally not available for free. Below is a list of vendors which have passed our quality screening (in total, we screened over a dozen vendors). To qualify, the vendor must aggregate data from all US national/regional exchanges as only complete datasets are suitable for research use. The last point is especially important as there are many vendors who just get data from a couple sources and is missing important information such as dark pool trades. They offer some alternatives for free data: Daily Resolution Data 1) Yahoo! Finance– Daily resolution data, with split/dividend adjustments can be downloaded from here. The download procedure can be automated using this tool. Note, Yahoo quite frequently has errors in its database and does not contain data for delisted symbols. 2) QuantQuote Free Data– QuantQuote offers free daily resolution data for the S&P500 at this web page under the Free Data tab. The data accounts for symbol changes, splits, and dividends, and is largely free of the errors found in the Yahoo data. Note, only 500 symbols are available unlike Yahoo which provides all listed symbols. And they list recommendations about who to buy the data from. "Market makers (shortened MM) in an exchange are generally required to list both a bid and ask price to allow both buyers and sellers to trade and keep the market moving.  However, a more general idea of a MM may includes companies off an exchange (say large banks acting as broker/dealers in an over-the-counter market) are not required to give a simultaneous bid/ask, but often will on request.  So, it might depend on where you are getting this data but likely the bid/ask was quoted simultaneously. An exchange, like the NASDAQ for instance, may have multiple MMs for a given market.  The ""market"" spread will be from the highest bid to the lowest ask over all the MMs.  The highest bid and lowest ask may come from different MMs and any particular MM often will have a larger spread. The size of the spread gives a rough idea of how much a MM is trying to make off of a ""round trip"" trade (buying than immediately selling to someone else or selling than immediately buying from someone else).  Of course, immediate round-trip trades are not always possible and there are many other complications.  However, half the spread is a rough indicator of how much they hope to make off of a single trade." 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 :) The S&P 500 is an index, you can't buy shares of an index, but you can find index funds to invest in. Each company in that fund that pays dividends will do so on their own schedule, and the fund you've invested in will either distribute dividends or accumulate them (re-invest), this is pre-defined, not something they'd decide quarter to quarter. If the fund distributes dividends, they will likely combine the dividends they receive and distribute to you quarterly.  The value you've referenced represents the total annual dividend across the index, dividend yield for S&P500 is currently ~1.9%, so if you invested $10,000 a year ago in a fund that matched the S&P 500, you'd have ~$190 in dividend yield. Have you looked at OptionsHouse?  They charge $2.95 per trade and are one of the lowest when it comes to fees.  Bare bones interface, but fast execution. Just a few observations within the Black-Scholes framework: Next, you can now use the Black-Scholes framework (stock price is a Geometric Brownian Motion, no transaction costs, single interest rate, etc. etc.) and numerical methods (such as a PDE solver) to price American style options numerically, but not with a simple closed form formula (though there are closed-form approximations). I tried direct indexing the S&amp;P500 myself and it was a lot of work. Lots of buys and sells to rebalance, tons of time in spreadsheets running calculations/monitoring etc, dealing with stocks being added or removed from the index, adding money (inflows). Etc. All of the work is the main reason I stopped. I came to realize the 0.05% I pay Vanguard is a great deal. "Yes. S&P/ Case-Shiller real-estate indices are available, as a single national index as well as multiple regional geographic indices. These indices are updated on the last Tuesday of every month. According to the Case-Shiller Index Methodology documentation: Their purpose is to measure the average change in home prices in 20 major metropolitan areas... and three price tiers– low, middle and high. The regional indices use 3-month moving averages, published with a two-month lag. This helps offset delays due to ""clumping"" in the flow of sales price data from county deed recorders. It also assures sufficient sample sizes.  Regional Case-Shiller real-estate indices  * Source: Case-Shiller Real-estate Index FAQ. The S&P Case-Shiller webpage has links to historical studies and commentary by Yale University Professor Shiller. Housing Views posts news and analysis for the regional indices. Yes. The CME Group in Chicago runs a real-estate futures market. Regional S&P/ Case-Schiller index futures and options are   the first [security type] for managing U.S. housing risk. They    provide protection, or profit, in up or down markets. They extend to the   housing industry the same tools, for risk management and investment,    available for agriculture and finance. But would you want to invest? Probably not. This market has minimal activity. For the three markets, San Diego, Boston and Los Angeles on 28 November 2011, there was zero trading volume (prices unchanged), no trades settled, no open interest, see  far right, partially cut off in image below.  * Source: Futures and options activity[PDF] for all 20 regional indices.  I don't know the reason for this situation. A few guesses: Additional reference: CME spec's for index futures and options contracts." Bid and ask prices are the reigning highest buy price and lowest sell price in the market which doesn't mean one must only buy/sell at thise prices. That said one can buy/sell at whatever price they so wish although doing it at any other price than the bid/ask is usually harder as other market participants will gravitate to the reigning bid/ask price. So in theory you can buy at ask and sell at bid, whether or not your order will be filled is another matter altogether. The S&P is cap-weighted. So it's not as simple as buying 1 share of each of 500 stocks. (If it were, getting started might be doable, although adding to your position would take time and another large unit of money.) Can you do it? Sure? Do you have enough money to actually do it? I don't know. I'm happy to pay my .02-.03% to not worry about such things.