What does the average log-return value of a stock mean?
"Probably the best way to investigate this is to look at an example. First, as the commenters above have already said, the log-return from one period is log(price at time t/price at time t-1) which is approximately equal to the percentage change in the price from time t-1 to time t, provided that this percentage change is not big compared to the size of the price. (Note that you have to use the natural log, ie. log to the base e -- ln button on a calculator -- here.) The main use of the log-return is that is a proxy for the percentage change in the price, which turns out to be mathematically convenient, for various reasons which have mostly already been mentioned in the comments. But you already know this; your actual question is about the average log-return over a period of time. What does this indicate about the stock? The answer is: if the stock price is not changing very much, then the average log-return is about equal to the average percentage change in the price, and is very easy and quick to calculate. But if the stock price is very volatile, then the average log-return can be wildly different to the average percentage change in the price. Here is an example: the closing prices for Pitchfork Oil from last week's trading are: 10, 5, 12, 5, 10, 2, 15. The percentage changes are: -0.5, 1.4, -0.58, 1, -0.8, 6.5 (where -0.5 means -50%, etc.) The average percentage change is 1.17, or 117%. On the other hand, the log-returns for the same period are -0.69, 0.88, -0.88, 0.69, -1.6, 2, and the average log-return is about 0.068. If we used this as a proxy for the average percentage change in the price over the whole seven days, we would get 6.8% instead of 117%, which is wildly wrong. The reason why it is wrong is because the price fluctuated so much. On the other hand, the closing prices for United Marshmallow over the same period are 10, 11, 12, 11, 12, 13, 15. The average percentage change from day to day is 0.073, and the average log-return is 0.068, so in this case the log-return is very close to the percentage change. And it has the advantage of being computable from just the first and last prices, because the properties of logarithms imply that it simplifies to (log(15)-log(10))/6. Notice that this is exactly the same as for Pitchfork Oil. So one reason why you might be interested in the average log-return is that it gives a very quick way to estimate the average return, if the stock price is not changing very much. Another, more subtle reason, is that it actually behaves better than the percentage return. When the price of Pitchfork jumps from 5 to 12 and then crashes back to 5 again, the percentage changes are +140% and -58%, for an average of +82%. That sounds good, but if you had bought it at 5, and then sold it at 5, you would actually have made 0% on your money. The log-returns for the same period do not have this disturbing property, because they do add up to 0%.  What's the real difference in this example? Well, if you had bought $1 worth of Pitchfork on Tuesday, when it was 5, and sold it on Wednesday, when it was 12, you would have made a profit of $1.40. If you had then bought another $1 on Wednesday and sold it on Thursday, you would have made a loss of $0.58. Overall, your profit would have been $0.82. This is what the average percentage return is calculating. On the other hand, if you had been a long-term investor who had bought on Tuesday and hung on until Thursday, then quoting an ""average return"" of 82% is highly misleading, because it in no way corresponds to the return of 0% which you actually got!  The moral is that it may be better to look at the log-returns if you are a buy-and-hold type of investor, because log-returns cancel out when prices fluctuate, whereas percentage changes in price do not. But the flip-side of this is that your average log-return over a period of time does not give you much information about what the prices have been doing, since it is just (log(final price) - log(initial price))/number of periods. Since it is so easy to calculate from the initial and final prices themselves, you commonly won't see it in the financial pages, as far as I know.  Finally, to answer your question: ""Does knowing this single piece of information indicate something about the stock?"", I would say: not really. From the point of view of this one indicator, Pitchfork Oil and United Marshmallow look like identical investments, when they are clearly not. Knowing the average log-return is exactly the same as knowing the ratio between the final and initial prices." Log-returns are very commonly used in financial maths, especially quantitative finance.  The important property is that they're symmetrical around 0 with respect to addition. This property makes it possible to talk about an average return. For instance, if a stock goes down 20% over a period of time, it has to gain 25% to be back where you started.  For the log-return on the other hand the numbers are 0.223 down over a period of time, and 0.223 up to get you back to square 1. In this sense, you can simply take an arithmetic average and it makes sense.  You can freely add up or subtract values on the log-return scale, like log-interest rates or log-inflation rates.  Whereas the arithmetic mean of (non-log) returns is simply meaningless: A stock with returns -3% and +3% would have 0% on average, when in fact the stock has declined in price? The correct approach on direct price-returns would be to take a different mean (e.g. geometric) to get a decent average.  And yet it will be hard to incorporate other information, like subtracting the risk-free rate or the inflation rate to get rate-adjusted average returns. In short: Log-returns are easier to handle computationally, esp. in bulk, but non-log-returns are easier to comprehend/imagine as a number of their own. Knowing the log return is useful - the log return can help you to work out the annual return over the period it was estimated - and this should be comparable between stocks. One should just be careful with the calculation so that allowance for dividends is made sensibly.
&gt; The stock market measures individual companies' ups and downs, right?  Not precisely, no. If anything it measures...  1. Information  2. Risk and Riskiness  3. Market Sentiment  &gt; Perhaps it could even gain over my life.  One would assume that this would be a relatively flat graph, with little if any trend, and occasional spikes upwards and downwards. It'd also be subject to caps and floors, unlike the market which is only floored (at 0).  &gt; I don't know if anyone could come up with a kind of standardised measurement we could use to do this.  It'd be impossible. Happiness is subjective *and* relative. Getting a million bucks might make me happy, but Bill Gates bored. Having a child can be conflicting intensely. The death of a loved one could be both sad and a relief. The net return reported to you (as a percentage) by a mutual fund is the gross return minus the expense ratio.  So, if the gross return is X% and the expense ratio is Y%, your account will show a return of (X-Y)%.  Be aware that X could be negative too. So, with Y = 1, If X = 10 (as you might get from a stock fund if you believe historical averages will continue), then the net return is 9% and you have lost (Y/X) times 100% = 10% of the gross return. If X = 8 (as you might get from a bond fund if you believe historical averages will continue), then the net return is 7% and you have lost (Y/X) times 100% = 12.5% of the gross return. and so on and so forth.  The numbers used are merely examples of the returns that have been obtained historically, though it is worth emphasizing that 10% is an average return, averaged over many decades, from investments in stocks, and to believe that one will get a 10% return year after year is to mislead oneself very badly. I think the point of the illustrations is that expense ratios are important, and should matter a lot to you, but that their impact is proportionately somewhat less if the gross return  is high, but very significant if the gross return is low, as  in money-market funds.  In fact, some money market funds which  found that X < Y have even foregone charging the expense ratio  fee so as to maintain a fixed $1 per share price.  Personally,  I would need a lot of persuading to invest in even a stock fund with 1% expense ratio. "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:" Let's use an example: You buy 10 machines for 100k, and those machines produce products sold for a total of 10k/year in profit (ignoring labor/electricity/sales costs etc). If the typical investor requires a rate of return of 10% on this business, your company would be worth 100k.  In investing terms, you would have a PE ratio of 10.  The immediately-required return will be lower if substantially greater returns are expected in the future (expected growth), and the immediately required return will be higher if your business is expected to shrink. If at the end of the year you take your 10k and purchase another machine, your valuation will rise to 110k, because you can now produce 11k in earnings per year.  If your business has issued 10,000 shares, your share price will rise from $10 to $11.  Note that you did not just put cash in the bank, and that you now have a higher share price. At the end of year 2, with 11 machines, lets imagine that customer demand has fallen and you are forced to cut prices.  You somehow produce only 10k in profit, instead of the anticipated 11k.  Investors believe this 10k in annual profit will continue into the forseable future.  The investor who requires 10% return would then only value your company at 100k, and your share price would fall back from $11 to $10.  If your earnings had fallen even further to 9k, they might value you at 90k (9k/0.1=$90k).  You still have the same machines, but the market has changed in a way that make those machines less valuable. If you've gone from earning 10k in year one with 10 machines to 9k in year two with 11 machines, an investor might assume you'll make even less in year three, potentially only 8k, so the value of your company might even fall to 80k or lower.  Once it is assumed that your earnings will continue to shrink, an investor might value your business based on a higher required rate of return (e.g. maybe 20% instead of 10%), which would cause your share price to fall even further. "For a retail investor who isn't a Physics or Math major, the ""Beta"" of the stock is probably the best way to quantify risk.  Examples: A Beta of 1 means that a stock moves in line with the market. Over 1 means that you would expect the stock to move up or down faster than the market as a whole. Under 1 means that you would expect the stock to move slower than the market as a whole." There are books on the subject of valuing stocks. P/E ratio has nothing directly to do with the value of a company. It may be an indication that the stock is undervalued or overvalued, but does not indicate the value itself. The direct value of company is what it would fetch if it was liquidated. For example, if you bought a dry cleaner and sold all of the equipment and receivables, how much would you get? To value a living company, you can treat it like a bond. For example, assume the company generates $1 million in profit every year and has a liquidation value of $2 million. Given the risk profile of the business, let's say we would like to make 8% on average per year, then the value of the business is approximately $1/0.08 + $2 = $14.5 million to us. To someone who expects to make more or less the value might be different. If the company has growth potential, you can adjust this figure by estimating the estimated income at different percentage chances of growth and decline, a growth curve so to speak. The value is then the net area under this curve.  Of course, if you do this for NYSE and most NASDAQ stocks you will find that they have a capitalization way over these amounts. That is because they are being used as a store of wealth. People are buying the stocks just as a way to store money, not necessarily make a profit. It's kind of like buying land. Even though the land may never give you a penny of profit, you know you can always sell it and get your money back. Because of this, it is difficult to value high-profile equities. You are dealing with human psychology, not pennies and dollars. Don't know the name but it means you're long with conviction :P  Unlimited gains, maximum loss of 95$  + (8-6) = 97$.  Basically You are long @ 107  - -2 from 105 to 95.  You would have to be ULTRA bullish to initiate this strategy. "Yes - this is exactly what it means.  No losses (negative earnings).   With today's accounting methods, you might want to determine whether you view earnings including or excluding extraordinary items.   For example, a company might take a once-off charge to its earnings when revising the value of a major asset.  This would show in the ""including"" but not in the ""excluding"" figure.   The book actually has a nice discussion in Chapter 12 ""Things to Consider About Per-Share Earnings"" which considers several additional variables to consider here too. Note that this earnings metric is different from ""Stock Selection for the Defensive Investor"" which requires 10 years. PS - My edition (4th edition hardback) doesn't have 386 pages so your reference isn't correct for that edition.  I found it on page 209 in Chapter 15 ""Stock Selection for the Enterprising Investor""." I was thinking that the value of the stock is the value of the stock...the actual number of shares really doesn't matter, but I'm not sure. You're correct.  Share price is meaningless.   Google is $700 per share, Apple is $100 per share, that doesn't say anything about either company and/or whether or not one is a better investment over the other. You should not evaluate an investment decision on price of a share.  Look at the books decide if the company is worth owning, then decide if it's worth owning at it's current price. None of the above. The fair value is a term used to describe an analytical result of projecting the company's future dividends and profits into a present value.  Such estimates are published by the likes of Morningstar, S&P and Value Line.  It is quite common for a stock to trade well above or below such estimated fair values. "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." I didn't mean to imply that the perceived value of a company on the stock market somehow proved that the companies had not lost capital or value. But it sure is a clear datapoint to juxtapose against all of the other hard facts in play. Often, the stock market isn't wrong... even if it may lag. If these companies have all this loss, is that baked into the current price? But again I was just merely grasping for the details from the plethora of sources given. I surely missed the real meat of the data. How I understand it is: supply/demand affect price of stock   negatively/positively, respectively. Correct. Volume is the amount of buying/selling activity in these stocks (more   volume = more fluctuation, right?). Sort of.  Higher volume means higher liquidity.  That is, a stock that is traded more is easier to trade.  It doesn't necessarily mean more fluctuation and in the real world, it often means that these are well-understood stocks with a high amount of analyst coverage.  This tends towards these stocks not being as volatile as smaller stocks with less liquidity. Company revenue (and profit) will help an investor predict company   growth. That is one factor in a stock price.  There are certain stocks that you would buy without them making a profit because their future revenue looks potentially explosive.  However, these stocks are very risky and are bubble-prone. If you're starting out in the share market, it's generally a good idea to invest in index funds (I am not a broker, my advice should not be taken as financial advice).  These funds aggregate risk by holding a lot of different companies.  Also, statistics have shown that over time, buying and holding index funds long term tends to dramatically outperform other investment strategies, particularly for people with low amounts of capital. The information on GOOG or other sites is the average price of the stock and is indicative of the price at with the stock would be available. The actual trades happen at different values throught the day ...  So the prices are good for most purposes and if you need the exact prices, you can thne decided to log into you trading terminal and get the actual quotes   This is similar to FX quotes or any other such quotes and give you a general sense The mortgage and title of the house would be under both your names equally.  When I applied for a mortgage with my girlfriend, I was the primary applicant because of my credit score and she was the secondary because of her income (she makes more).  When all was said and done, it was explained to us that the mortgage was ours equally and so was the house, and that I didn't hold more ownership than her over either.  We were approved quickly and hassle free. This is our first house too. This is in Florida.