Why IV and stock price are inversely related
"people are willing to pay higher premiums for options when stocks go down. Obviously the time value and intrinsic value and interests rates of the option doesn't change because of this so the miscalculation remainder is priced into the implied volatility part of the formula.  Basically, anything that suggests the stock price will get volatile (sharp moves in either direction) will increase the implied volatility of the option. For instance, around earnings reports, the IV in both calls and puts in the nearest expiration dates are very high. When stocks go down sharply, the volatility is high because some people are buying puts for protection and others are buying calls because they think there will be a rebound move in the other direction. People (the ""sleep-at-night"" investors, not the derivatives traders ;) )  tend to be calm when stocks are going up, and fearful when they are going down. The psychology is important to understand and observe and profit from, not to quantitatively prove. The first paragraph should be your qualitative answer"
"There are two primary reasons shares are sold short:  (1) to speculate that a stock's price will decline and (2) to hedge some other related financial exposure. The first is acknowledged by the question.  The second reason may be done for taxes (shorting ""against the box"" was once permitted for tax purposes), for arbitrage positions such as merger arbitrage and situations when an outright sale of stock is not permitted, such as owning restricted stock such as employer-granted shares. Why would a shareholder lend the investor the shares? The investor loaning his stock out to short-sellers earns interest on those shares that the borrower pays.  It is not unusual for the annualized cost of borrowing stock to be double digits when there is high demand for heavily shorted shares.  This benefit is however not available to all investors." "You are correct that, barring an equity capital raise, your money doesn't actually end up in the company. However, interest in their stock can help a company in other ways; Management/board members hopefully own shares or options themselves, thus knowing that ""green"" policies are favorable for the stock price (as your fund might buy shares) can be quite an incentive for them to go green(er).  Companies with above average company share performance are also often viewed as financially healthy and so creditors tend to charge lower interest for companies with good share performance.  Lastly, a high share price makes a company difficult to take over (as all those shares have to be acquired) and at the same time makes it easier for the company to perform takeovers themselves as they can finance such acquisitions by issuing more of their own shares. There is also the implication that money flowing towards such green companies is money flowing out of/away from polluting companies, for these ""dirty"" companies the inverse of the previous points can hold true. Of course on the other hand there is quite an argument to be made that large enough ""green"" funds should actually buy substantial positions in companies with poor environmental records and steer the company towards greener policies but that might be a hard sell to investors." "It's been said before, but to repeat succinctly, a company's current share price is no more or less than what ""the market"" thinks that share is worth, as measured by the price at which the shares are being bought and sold. As such, a lot of things can affect that price, some of them material, others ethereal. A common reason to own stock is to share the profits of the company; by owning 1 share out of 1 million shares outstanding, you are entitled to 1/1000000 of that company's quarterly profits (if any). These are paid out as dividends. Two key measurements are based on these dividend payments; the first is ""earnings per share"", which is the company's stated quarterly profits, divided by outstanding shares, with the second being the ""price-earnings ratio"" which is the current price of the stock divided by its EPS. Your expected ""yield"" on this stock is more or less the inverse of this number; if a company has a P/E ratio of 20, then all things being equal, if you invest $100 in this stock you can expect a return of $5, or 5% (1/20). As such, changes in the expected earnings per share can cause the share price to rise or fall to maintain a P/E ratio that the pool of buyers are willing to tolerate. News that a company might miss its profit expectations, due to a decrease in consumer demand, an increase in raw materials costs, labor, financing, or any of a multitude of things that industry analysts watch, can cause the stock price to drop sharply as people look for better investments with higher yields. However, a large P/E ratio is not necessarily a bad thing, especially for a large stable company. That stability means the company is better able to weather economic problems, and thus it is a lower risk. Now, not all companies issue dividends. Apple is probably the most well-known example. The company simply retains all its earnings to reinvest in itself. This is typically the strategy of a smaller start-up; whether they're making good money or not, they typically want to keep what they make so they can keep growing, and the shareholders are usually fine with that. Why? Well, because there's more than one way to value a company, and more than one way to look at a stock. Owning one share of a stock can be seen quite literally as owning a share of that company. The share can then be valued as a fraction of the company's total assets.  Sounds simple, but it isn't, because not every asset the company owns has a line in the financial statements. A company's brand name, for instance, has no tangible value, and yet it is probably the most valuable single thing Apple owns. Similarly, intellectual property doesn't have a ""book value"" on a company's balance sheet, but again, these are huge contributors to the success and profitability of a company like Apple; the company is viewed as a center of innovation, and if it were not doing any innovating, it would very quickly be seen as a middleman for some other company's ideas and products. A company can't sustain that position for long even if it's raking in the money in the meantime. Overall, the value of a company is generally a combination of these two things; by owning a portion of stock, you own a piece of the company's assets, and also claim a piece of their profits. A large company with a lot of material assets and very little debt can be highly valued based solely on the sum of its parts, even if profits are lagging. Conversely, a company more or less operating out of a storage unit can have a patent on the cure for cancer, and be shoveling money into their coffers with bulldozers." "Let me start with a somewhat sarcastic statement: There are probably as many things done to analyze a stock as there are people doing the analysis! That said, at a general level an analyst researches the historical performance of the company at a fairly detailed level (operations within divisions of the company, product development cycles within divisions, expenses vs income trends for each division and product, marketing costs, customer acquisition costs, etc); gathers information about what the company is doing now AND planning to do in the future -- often by a discussion with principles at the company; establishes a view on related macro-economic trends, sector and industry trends, demographic trends, etc.; and combines it all to forecast a change in revenues, margins, free cash flow, dividends, etc. over a period of time.   They then apply statistics that relate those numbers to stock price in order to imply stock prices and price ranges over those same periods.  Finally, depending on how those stock prices compare to the current stock price, they'll classify the stock as Buy, Sell, Hold, etc. This sounds like alot of work.   And it generally is if you get detailed about it, which is what professionals or significant money managers are doing.   However, there are also lots of arm-chair analysts posting their output on any number of financial sites (Seeking Alpha, Motley Fool, etc.) if you'd like to really explore the range of detail some people consider as a ""stock analysis"".  That sounds more negative than I intended it to be, so let me clarify that I think some of these write-ups are really quite good IMO." Companies do both quite often.  They have opposite effects on the share price, but not on the total value to the shareholders.  Doing both causes value to shareholders to rise (ie, any un-bought back shares now own a larger percentage of the company and are worth more) and drops the per-share price (so it is easier to buy a share of the stock).  To some that's irrelevant, but some might want a share of an otherwise-expensive stock without paying $700 for it. As a specific example of this, Apple (APPL) split its stock in 2014 and also continued a significant buyback program: Apple announces $17B repurchase program, Oct 2014 Apple stock splits 7-to-1 in June 2014. This led to their stock in total being worth more, but costing substantially less per share. As yet another explanation of why it does not really matter, you can look at this from the valuation point of view. Stock price is the present value of its future cash flows (be it free cash flow of the firm or dividends, depending on the model). Let's have a look at the dividends case. Imagine, the price of the stock is based on only three dividends streams $5 dollars each: dividend to be paid today, in year 1, and in year 2. Each should be discounted back to today (say, at 10%), except today's dividend, since today is now.  Once that dividend is paid, it is no longer in the stream of cash flows. So if we just delete that first $5 from the formula, the price will adjust itself down by the amount of the dividend to $8.68. NOTE that this is a very simple example, since in reality cash flows streams are arguably infinite and because there are many other factors affecting stock price. But simply for your understanding, this example should provide you with the reason simply from the valuation perspective. No, I think you are misunderstanding the Math. Stock splits are a way to control relatively where the price per share can be for a company as companies can split or reverse split shares which would be similar to taking dimes and giving 2 nickels for each dime, each is 10 cents but the number of coins has varied. This doesn't create any additional value since it is still 10 cents whether it is 1 dime or 2 nickels.  Share repurchase programs though are done to prevent dilution as executives and those with incentive-stock options may get shares in the company that increase the number of outstanding shares that would be something to note. 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.