Why does the stock market index get affected when a terrorist attack takes place?
"There are more than a few different ways to consider why someone may have a transaction in the stock market: Employee stock options - If part of my compensation comes from having options that vest over time, I may well sell shares at various points because I don't want so much of my new worth tied up in one company stock. Thus, some transactions may happen from people cashing out stock options. Shorting stocks - This is where one would sell borrowed stock that then gets replaced later. Thus, one could reverse the traditional buy and sell order in which case the buy is done to close the position rather than open one. Convertible debt - Some companies may have debt that come with warrants or options that allow the holder to acquire shares at a specific price. This would be similar to 1 in some ways though the holder may be a mutual fund or company in some cases. There is also some people that may seek high-yield stocks and want an income stream from the stock while others may just want capital appreciation and like stocks that may not pay dividends(Berkshire Hathaway being the classic example here). Others may be traders believing the stock will move one way or another in the short-term and want to profit from that. So, thus the stock market isn't necessarily as simple as you state initially. A terrorist attack may impact stocks in a couple ways to consider: Liquidity - In the case of the attacks of 9/11, the stock market was closed for a number of days which meant people couldn't trade to convert shares to cash or cash to shares. Thus, some people may pull out of the market out of fear of their money being ""locked up"" when they need to access it. If someone is retired and expects to get $x/quarter from their stocks and it appears that that may be in jeopardy, it could cause one to shift their asset allocation. Future profits - Some companies may have costs to rebuild offices and other losses that could put a temporary dent in profits. If there is a company that makes widgets and the factory is attacked, the company may have to stop making widgets for a while which would impact earnings, no? There can also be the perception that an attack is ""just the beginning"" and one could extrapolate out more attacks that may affect broader areas. Sometimes what recently happens with the stock market is expected to continue that can be dangerous as some people may believe the market has to continue like the recent past as that is how they think the future will be." While JB King says some useful things, I think there is another fundamental reason why stock markets go down after disasters, either natural or man-made.  There is a real impact on the markets - in the case of something like 9/11 due to closed airport, higher security costs, closer inspections on trade goods, tighter restrictions on visas, real payments for the rebuilding of destroyed buildings and insurance payouts for killed people, and eventually the cost of a war. But almost as important is the uncertainty and risk. Nobody knew what was going to happen in the days and weeks after an attack like that. Is there going to be another one a week later, or every week for the next year? Will air travel become essentially impractical? Will international trade be severely restricted? All those would have a huge, massive effect on the economy. You may argue that those things are very unlikely, even after something like 9/11. But even a small increase in the likelihood of a catastrophic economic crash is enough to start people selling. There is another thing that drives the market down. Even if most people are sure that there won't be a catastrophic economic crash, they know that other people think there might be and so will sell. That will drive the market down. If they know the market is going down, then sensible traders will start to sell, even if they think there is zero risk of a crash. This makes the effect worse. Eventually prices will drop so far that the people who don't think there is a crash will start to buy, so they can make a profit on the recovery. But that usually doesn't happen until there has been a substantial drop.
A stock's price does not move in a completely continuous fashion.  It moves in discrete steps depending on who is buying/selling at given prices. I'm guessing that by opening bell the price for buying/selling a particular stock has changed based on information obtained overnight. A company's stock closes at $40.  Overnight, news breaks that the company's top selling product has a massive defect.  The next morning the market opens.  Are there any buyers of the stock at $40?  Probably not.  The first trade of the stock takes place at $30 and is thus, not the same as the previous day's close. Yes, you've got it right.  The change in price is less meaningful as the instrument is further from the price of the underlying.  As the delta moves less, the gamma is much less. Gamma is to delta as acceleration is to speed.  Speed is movement relative to X, and acceleration is rate of change in speed.  Delta is movement relative to S, and gamma is the rate of change in delta. Delta changes quickly when it is around the money, which is another way of saying gamma is higher.  Delta is the change of the option price relative to the change in stock price.  If the strike price is near the market price, then the odds of being in or out of the money could appear to be changing very quickly - even going back and forth repeatedly. Gamma is the rate of change of the delta, so these sudden lurches in pricing are by definition the gamma.  This is to some extent a little mundane and even obvious.  But it's a useful heuristic for analyzing prices and movement, as well as for focusing analyst attention on different pricing aspects. You've got it right.  If delta is constant (zero 'speed' for the change in price) then gamma is zero (zero 'acceleration'). 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. For example, if the Dow, S&P 500, NASDAQ are all down does that necessarily mean the Canadian stock will get negatively impacted? Or is it primarily impacted by the Canadian market? The TWMJF stock makes up a very small part of the Canadian market so it affects the overall market, but this doesn't mean that the overall market affects this stock. So then the answer is: no, the TWMJF stock price will not necessarily follow either US or Canadian market indexes.  However, there can be major events which can affect the markets, including the stocks which make up the markets. TWMJF will probably be more sensitive to Canadian events than US events. The opening price is derived from new information received. It reflects the current state of the market. Opening Price Deviation (from Investopedia): Investor expectation can be changed by corporate announcements or   other events that make the news. Corporations typically make   news-worthy announcements that may have an effect on the stock price   after the market closes. Large-scale natural disasters or man-made   disasters such as wars or terrorist attacks that take place in the   afterhours may have similar effects on stock prices. When this   happens, some investors may attempt to either buy or sell securities   during the afterhours. Not all orders are executed during after-hours trading. The lack of   liquidity and the resulting wide spreads make market orders   unattractive to traders in after-hours trading. This results in a   large amount of limit or stop orders being placed at a price that is   different from the prior day’s closing price. Consequently, when the   market opens the next day, a substantial disparity in supply and   demand causes the open to veer away from the prior day’s close in the   direction that corresponds to the effect of the announcement, news or   event. Graphs are nothing but a representation of data. Every time a trade is made, a point is plotted on the graph. After points are plotted, they are joined in order to represent the data in a graphical format.  Think about it this way.  1.) Walmart shuts at 12 AM. 2.)Walmart is selling almonds at $10 a pound.  3.) Walmart says that the price is going to reduce to $9 effective tomorrow. 4.) You are inside the store buying almonds at 11:59 PM.  5.) Till you make your way up to the counter, it is already 12:01 AM, so the store is technically shut. 6.) However, they allow you to purchase the almonds since you were already in there.  7.) You purchase the almonds at $9 since the day has changed. 8.) So you have made a trade and it will reflect as a point on the graph. 9.) When those points are joined, the curves on the graph will be created. 10.) The data source is Walmart's system as it reflects the sale to you. ( In your case the NYSE exchange records this trade made). Buying a stock is just like buying almonds. There has to be a buyer. There has to be a seller. There has to be a price to which both agree. As soon as all these conditions are met, and the trade is made, it is reflected on the graph. The only difference between the graphs from 9 AM-4 PM, and 4 PM-9 AM is the time. The trade has happened regardless and NYSE(Or any other stock exchange) has recorded it! The graph is just made from that data. Cheers. During the 12 plus hours the market was closed news can change investors opinion of the stock. When the market reopens that first trade could be much different than the last trade the day before. As others have pointed out, the value of Apple's stock and the NASDAQ are most likely highly correlated for a number of reasons, not least among them the fact that Apple is part of the NASDAQ. However, because numerous factors affect the entire market, or at least a significant subset of it, it makes sense to develop a strategy to remove all of these factors without resorting to use of an index. Using an index to remove the effect of these factors might be a good idea, but you run the risk of potentially introducing other factors that affect the index, but not Apple. I don't know what those would be, but it's a valid theoretical concern.  In your question, you said you wanted to subtract them from each other, and only see an Apple curve moving around a horizontal line. The basic strategy I plan to use is similar but even simpler. Instead of graphing Apple's stock price, we can plot the difference between its stock price on business day t and business day t-1, which gives us this graph, which is essentially what you're looking for:  While this is only the preliminaries, it should give you a basic idea of one procedure that's used extensively to do just what you're asking. I don't know of a website that will automatically give you such a metric, but you could download the price data and use Excel, Stata, etc. to analyze this.  The reasoning behind this methodology builds heavily on time series econometrics, which for the sake of simplicity I won't go into in great detail, but I'll provide a brief explanation to satisfy the curious. In simple econometrics, most time series are approximated by a mathematical process comprised of several components: In the simplest case, the equations for a time series containing one or more of the above components are of the form that taking the first difference (the procedure I used above) will leave only the random component. However, if you want to pursue this rigorously, you would first perform a set of tests to determine if these components exist and if differencing is the best procedure to remove those that are present. Once you've reduced the series to its random component, you can use that component to examine how the process underlying the stock price has changed over the years. In my example, I highlighted Steve Jobs' death on the chart because it's one factor that may have led to the increased standard deviation/volatility of Apple's stock price. Although charts are somewhat subjective, it appears that the volatility was already increasing before his death, which could reflect other factors or the increasing expectation that he wouldn't be running the company in the near future, for whatever reason. My discussion of time series decomposition and the definitions of various components relies heavily on Walter Ender's text Applied Econometric Time Series. If you're interested, simple mathematical representations and a few relevant graphs are found on pages 1-3. Another related procedure would be to take the logarithm of the quotient of the current day's price and the previous day's price. In Apple's case, doing so yields this graph:  This reduces the overall magnitude of the values and allows you to see potential outliers more clearly. This produces a similar effect to the difference taken above because the log of a quotient is the same as the difference of the logs The significant drop depicted during the year 2000 occurred between September 28th and September 29th, where the stock price dropped from 26.36 to 12.69. Apart from the general environment of the dot-com bubble bursting, I'm not sure why this occurred. Another excellent resource for time series econometrics is James Hamilton's book, Time Series Analysis. It's considered a classic in the field of econometrics, although similar to Enders' book, it's fairly advanced for most investors.  I used Stata to generate the graphs above with data from Yahoo! Finance: There are a couple of nuances in this code related to how I defined the time series and the presence of weekends, but they don't affect the overall concept. For a robust analysis, I would make a few quick tweaks that would make the graphs less appealing without more work, but would allow for more accurate econometrics. 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? The major reason for the market retreating is the uncertainty regarding the US Dollar. If the US credit rating drops that will have an inflationary effect on the currency (as it will push up the cost of US Treasuries and reduce confidence in the USD). If this continues the loss of USD confidence could bring an end to the USD as the world's reserve currency which could also create inflation (as world banks could reduce their USD reserves). This can make US assets appear overvalued. Why is there such a large emphasis on   the S&P rating? S&P is a large trusted rating agency so the market will respond to their analysis much like how a bank would respond to any change in your rating by Transunion (Consumer Credit Bureau) Does this have any major implications   for the US stock markets today, in the   short term and in July? If you are a day-trader I'm sure it does. There will be minor fluctuations in the market as soon as news comes out (either of its extension or any expected delays in passing that extension). What happens when the debt ceiling is   reached? Since the US is in a deficit spending situation it needs to borrow more to satisfy its existing obligations (in short it pays its debt with more debt). As a result, if the debt ceiling isn't raised then eventually the US will be unable to pay its existing obligations. We would be in a default situation which could have devastating affects on the value of the USD. How hard the hit will depend on how long the default situation lasts (the longer we go without an increased ceiling after the exhaustion point the more we default on). In reality, Congress will approve a raise, but they will drag it out to the last possible minute. They want to appear as if they are against it, but they understand the catastrophic effects of not doing so. Stocks, gold, commodities, and physical real estate will not be affected by currency changes, regardless of whether those changes are fast or slow.  All bonds except those that are indexed to inflation will be demolished by sudden, unexpected devaluation. Notice: The above is true if devaluation is the only thing going on but this will not be the case.  Unfortunately, if the currency devalued rapidly it would be because something else is happening in the economy or government.  How these asset values are affected by that other thing would depend on what the other thing is.  In other words, you must tell us what you think will cause devaluation, then we can guess how it might affect stock, real estate, and commodity prices. The All Ords Index consists of the 500 largest companies by market capitalisation listed on the Australia Stock Exchange.  Each stock in the All Ords. Index is given a weighting based on its market capitalisation. As the price of the stocks within the All Ords. Index change, so does the points on the index itself.  The Index is more sensitive to changes in the larger capitalised stocks due to their larger weighting in the Index. Example: If a company has a weighting of 10% and its price goes up by 10%, and all other stocks in the Index don't go up or down, then this will cause the All Ords Index to go up by 1% (10% of 10%). "Stock price is set to the price with the highest transaction volume at any given time.  The stock price you cited was only valid in the last transaction on a specific stock exchange. As such it is more of an ""historic"" value. Next trade will be done with the next biggest volume. Depending on the incoming bids and asks this could be higher or lower, but you can assume it will not be too far off if there is no crash underway. Simple example stock exchange:" You can definitely affect the price - putting in a buy increases the demand for the stock, causing a permanent price move.  Also if you hammer the market trying to execute too quickly you can hit offers that are out of the money and move the price temporarily before it stabilizes to its new equilibrium.   True, as an individual investor your trades will be negligible in size and the effect will be nonexistent. But if you are a hedge fund putting in a buy for 5% of dtv,  you can have a price impact. not 50%, but at least a handful of bps. If you are in a position to have information that will impact the shares of a stock or index fund and you use that information for either personal gain or to mitigate the losses that you would have felt then it is insider trading.  Even if in the end your quiet period passes with little or no movement of the stocks in question.  It is the attempt to benefit from or the appearance of the attempt to benefit from inside information that creates the crime.  This is the reason for the quiet periods to attempt to shield the majority of the companies employees from the appearance of impropriety, as well as any actual improprieties. With an index you are running a double edged sword because anything that is likely to cause APPLE to drop 10% is likely to give a bump to Motorola, Google, and its competitors.  So you could end up in jail for Insider trading and lose your shirt on a poor decision to short a Tech  ETF on knowledge that will cause Apple to take a hit.  It is certainly going to be harder to find the trade but the SEC is good at looking around for activity that is inconsistent with normal trading patterns of individuals in a position to have knowledge with the type of market impact you are talking about. It will depend largely on your broker what type of stop and trailing stop orders they provide. Saying that, I have not come across any brokers yet that offer limit orders with trailing stop orders.  Unlike a standard stop order where you can either make it a market stop order or a limit stop order, usually most brokers have trailing stop orders as market orders only, where you can either set the trailing stop to be a dollar value or percentage from the most recent high. Remember also, that trailing stop orders will be based on the intra-day highs and not the highest closing price. That means that if the share price spikes up during the day your trailing stop will move up, and if the price then spikes down you may be stopped out prematurely, after which the price might rally again. For this reason I try to base my trailing stops on the highest closing price by using standard stop loss orders and moving it up manually after the close of trade if the share price has closed at a new high. This takes a few minutes each evening (depending on how many stocks you have to check and adjust the stops for) but gives you more control. Using this method will also enable you to set limit orders attached to your stop loss triggers, and you won't have to keep your trailing too close to the last high price thus potentially causing you to get stopped out prematurely. Slightly off track but may be handy if you set profit targets, my broker has recently introduced Trailing Take Profit Orders. The way it works is, say you have a profit target of 50%, so you buy at $2 and want to take profits if the price reaches $3, you could set your Trailing Take Profit Trigger at say $3.10 or above and set a Trail by Amount of say $0.10. So if the price after hitting $3.10 falls to $3.00 you will be stopped out and collect your profits. If the price moves up to $3.30 and then falls to $3.20, you will be stopped out at $3.20 and make some extra profits. If the price continues going up the Trailing Take Profit will continue to move up always $0.10 below the highest price reached. I think this would be a very useful order if you were range trading where you could set the Trailing Take Profit trigger near recent resistance so you can get out if prices start reversing at or around the resistance, but continue profiting if the price breaks through the resistance.