Why do P/E ratios for a particular industry tend to cluster around particular values?
"This falls under value investing, and value investing has only recently picked up study by academia, say, at the turn of the millennium; therefore, there isn't much rigorous on value investing in academia, but it has started. However, we can describe valuations: In short, valuations are randomly distributed in a log-Variance Gamma fashion with some reason & nonsense mixed in. You can check for yourself on finviz.  You can basically download the entire US market and then some, with many financial and technical characteristics all in one spreadsheet. Re Fisher: He was tied for the best monetary economist of the 20th century and created the best price index, but as for stocks, he said this famous quote 12 days before the 1929 crash: ""Stock prices have reached what looks like a permanently high plateau. I do not feel there will be soon if ever a 50 or 60 point break from present levels, such as (bears) have predicted. I expect to see the stock market a good deal higher within a few months.""   - Irving Fisher, Ph.D. in economics, Oct. 17, 1929 EDIT Value investing has almost always been ignored by academia.  Irving Fisher and other proponents of it before it was codified by Graham in the mid 20th century certainly didn't help with comments like the above.  It was almost always believed that it was a sucker's game, ""the bigger sucker"" game to be more precise because value investors get destroyed during recession/collapses.  So even though a recessionless economy would allow value investors and everyone never to suffer spontaneous collapses, value investors are looked down upon by academia because of the inevitable yet nearly always transitory collapse.  This expresses that sentiment perfectly. It didn't help that Benjamin Graham didn't care about money so never reached the heights of Buffett who frequently alternates with Bill Gates as the richest person on the planet.  Buffett has given much credibility, and academia finally caught on around in 2000 or so after he was proven right about a pending tech collapse that nearly no one believed would happen; at least, that's where I begin seeing papers being published delving into value concepts.  If one looks harder, academia's even taken the torch and discovered some very useful tools. Yes, investment firms and fellow value investors kept up the information publishing, but they are not academics. The days of professors throwing darts at the stock listings and beating active managers despite most active managers losing to the market anyways really held back this side of academia until Buffett entered the fray and embarrassed them all with his club's performance, culminating in the Superinvestors article which is still relatively ignored.  Before that, it was the obsession with beta, the ratio of a security's variance to its covariance to the market, a now abandoned theory because it has been utterly discredited; the popularizers of beta have humorously embraced the P/B, not giving the satisfaction to Buffet by spurning the P/E.   Tiny technology firms receive ridiculous valuations because a long-surviving tiny tech firm usually doesn't stay small for long thus will grow at huge rates.  This is why any solvent and many insolvent tech firms receive large valuations: risk-adjusted, they should pay out huge on average.  Still, most fall by the wayside dead, and those 100 P/S valuations quickly crumble. Valuations are influenced by growth.  One can see this expressed more easily with a growing perpetuity: Where P is price, i is income, r is the rate of return, and g is the growth rate of i.  Rearranging, r looks like: Here, one can see that a higher P relative to i will dull the expected rate of return while a higher g will boost it. It's fun for us value investor/traders to say that the market is totally inefficient.  That's a stretch.  It's not perfectly inefficient, but it's efficient.  Valuations are clustered very tightly around the median, but there are mistakes that even us little guys can exploit and teach the smart money a lesson or two. If one were to look at a distribution of rs, one'd see that they're even more tightly packed.  So while it looks like P/Es are all over the place industry to industry, rs are much more well clustered. Tech, finance, and discretionaries frequently have higher growth rates so higher P/Es yet average rs.  Utilities and non-discretionaries have lower growth rates so lower P/Es yet average rs."
"Intrinsic value is a myth.  There is no such thing.  Subjective human demand is the only thing that gives anything value.  This subjectivity is different person to person and can change very quickly. Historically there are two main uses for gold: jewelry and money.  How can you tell when a particular type of money is undervalued?  It disappears from circulation since people prefer to use money that is overvalued.  This phenomenon is paraphrased in Gresham's Law: Bad money drives out good money. The Coinage Act of 1792 established the US dollar as 371.25 grains of silver or 24.75 grains of gold.  This established a government ratio of 15 ounces of silver to 1 ounce of gold.  In the late 18th century there was a large production of silver from Mexico and the market ratio of silver to gold increased to 15.75 to 1 by 1805.  The government ratio, however, was still 15 to 1.  This was enough incentive for people to exchange their silver coins for gold coins at the government ratio, melt the gold, and sell the gold bullion overseas at the market value.  Thus, gold coins disappeared from circulation as people either hoarded the gold or sent it abroad.  People used the overvalued silver coins (i.e. the ""bad"" money) domestically and gold coins disappeared from the market. In an attempt to correct the problem of disappearing gold coins the Coinage Act of 1834 was enacted.  It kept the US dollar at 371.25 grains of silver but changed the definition to 23.2 grains of gold which established a government ratio of 16 to 1.  This was close to the market ratio of gold to silver at the time so both gold and silver coins appeared in circulation again.  The gold rush of 1849 produced a lot of gold and the market ratio of silver to gold became 15.46 to 1.  Now gold was overvalued so people began exchanging their gold coins for silver coins at the government ratio, melt the silver, and sell the silver bullion overseas at the market value.  People used the overvalued gold coins (i.e. the ""bad"" money) domestically and silver coins disappeared from the market. When you see gold circulating everywhere you will know it is overvalued compared to other types of money.  Paper money always drives gold out of circulation since the market ratio of paper to gold severely under values gold. Source here." But they beat most revenue estimates... should be a heavy down day tomorrow, even though the stock is already massively oversold, especially when compared to industry peers and average P/E ratios of tech companies.  Last 12 months of earnings: $44.16 "You could not have two stocks both at $40, both with P/E 2, but one an EPS of $5 and the other $10.  EPS = Earnings Per Share P/E = Price per share/Earnings Per Share So, in your example, the stock with EPS of $5 has a P/E of 8, and the stock with an EPS of $10 has a P/E of 4.  So no, it's not valid way of looking at things, because your understanding of EPS and P/E is incorrect. Update: Ok, with that fixed, I think I understand your question better. This isn't a valid way of looking at P/E. You nailed one problem yourself at the end of the post: The tricky part is that you have to assume certain values remain   constant, I suppose But besides that, it still doesn't work. It seems to make sense in the context of investor psychology: if a stock is ""supposed to"" trade at a low P/E, like a utility, that it would stay at that low P/E, and thus a $1 worth of EPS increase would result in lower $$ price increase than a stock that was ""supposed to"" have a high P/E. And that would be true. But let's game it out: Scenario Say you have two stocks, ABC and XYZ. Both have $5 EPS. ABC is a utility, so it has a low P/E of 5, and thus trades at $25/share. XYZ is a high flying tech company, so it has a P/E of 10, thus trading at $50/share. If both companies increase their EPS by $1, to $6, and the P/Es remain the same, that means company ABC rises to $30, and company XYZ rises to $60. Hey! One went up $5, and the other $10, twice as much! That means XYZ was the better investment, right? Nope. You see, shares are not tokens, and you don't get an identical, arbitrary number of them. You make an investment, and that's in dollars. So, say you'd invested $1,000 in each. $1,000 in ABC buys you 40 shares. $1,000 in XYZ buys you 20 shares. Their EPS adds that buck, the shares rise to maintain P/E, and you have: ABC: $6 EPS at P/E 5 = $30/share. Position value = 40 shares x $30/share = $1,200 XYZ: $6 EPS at P/E 10 = $60/share. Position value = 20 shares x $60/share = $1,200 They both make you the exact same 20% profit. It makes sense when you think about it this way: a 20% increase in EPS is going to give you a 20% increase in price if the P/E is to remain constant. It doesn't matter what the dollar amount of the EPS or the share price is." You could sum the P/E ratio of all the companies in the industry and divide it by the number of companies to find the average P/E ratio of the industry.  Average P/E ratio of industry  = Sum of P/E ratio of all companies in   Industry / Number of companies in industry I have heard that people say the greater earning means greater   intrinsic value of the company. Then, the stock price is largely based   on the intrinsic value. So increasing intrinsic value due to   increasing earning will lead to increasing stock price. Does this make   sense ? Yes though it may be worth dissecting portions here. As a company generates earnings, it has various choices for what it can do with that money. It can distribute some to shareholders in the form of dividends or re-invest to generate more earnings. What you're discussing in the first part is those earnings that could be used to increase the perceived value of the company. However, there can be more than a few interpretations of how to compute a company's intrinsic value and this is how one can have opinions ranging from companies being overvalued to undervalued overall. Of Mines, Forests, and Impatience would be an article giving examples that make things a bit more complex. Consider how would you evaluate a mine, a forest or a farm where each gives a different structure to the cash flow? This could be useful in running the numbers here. Yes that is the case for the public company approach, but I was referring to the transaction approach:   Firm A and Firm B both have $100 in EBITDA. Firm A has $50 in cash, Firm B has $100 in cash.  Firm A sells for $500, Firm B sells for $600.  If we didn't subtract cash before calculating the multiple: Firm A: 5x Firm B: 6x  If we DO subtract cash before calculating the multiple: Firm A: 4.5x Firm B: 5x  So yea, subtracting cash does skew the multiple. "If you are looking for numerical metrics I think the following are popular: Price/Earnings (P/E) - You mentioned this very popular one in your question.  There are different P/E ratios - forward (essentially an estimate of future earnings by management), trailing, etc..  I think of the P/E as a quick way to grade a company's income statement (i.e: How much does the stock cost verusus the amount of earnings being generated on a per share basis?). Some caution must be taken when looking at the P/E ratio.  Earnings can be ""massaged"" by the company.  Revenue can be moved between quarters, assets can be depreciated at different rates, residual value of assets can be adjusted, etc..  Knowing this, the P/E ratio alone doesn't help me determine whether or not a stock is cheap. In general, I think an affordable stock is one whose P/E is under 15. Price/Book - I look at the Price/Book as a quick way to grade a company's balance sheet.  The book value of a company is the amount of cash that would be left if everything the company owned was sold and all debts paid (i.e. the company's net worth).  The cash is then divided amoung the outstanding shares and the Price/Book can be computed.  If a company had a price/book under 1.0 then theoretically you could purchase the stock, the company could be liquidated, and you would end up with more money then what you paid for the stock. This ratio attempts to answer: ""How much does the stock cost based on the net worth of the company?"" Again, this ratio can be ""massaged"" by the company.  Asset values have to be estimated based on current market values (think about trying to determine how much a company's building is worth) unless, of course, mark-to-market is suspended.  This involves some estimating.  Again, I don't use this value alone in determing whether or not a stock is cheap. I consider a price/book value under 10 a good number.   Cash - I look at growth in the cash balance of a company as a way to grade a company's cash flow statement.  Is the cash account growing or not? As they say, ""Cash is King"".  This is one measurement that can not be ""massaged"" which is why I like it.  The P/E and Price/Book can be ""tuned"" but in the end the company cannot hide a shrinking cash balance. Return Ratios - Return on Equity is a measure of the amount of earnings being generated for a given amount of equity (ROE = earnings/(assets - liabilities)).  This attempts to measure how effective the company is at generating earnings with a given amount of equity.  There is also Return on Assets which measures earnings returns based on the company's assets. I tend to think an ROE over 15% is a good number. These measurements rely on a company accurately reporting its financial condition.  Remember, in the US companies are allowed to falsify accounting reports if approved by the government so be careful.  There are others who simply don't follow the rules and report whatever numbers they like without penalty. There are many others.  These are just a few of the more popular ones.  There are many other considerations to take into account as other posters have pointed out." This is only a rule of thumb. Peter Lynch popularized it; the ratio PE/growth is often called the Lynch Ratio. At best it's a very rough guideline. I could fill up this page with other caveats. I'm not saying that it's wrong, only that it's grossly incomplete. For a 10 second eyeball valuation of growth stocks, it's fine. But that's the extent of its usefulness.