Efficient markets hypothesis and performance of IPO shares after lock-up period
There are rules that prevent two of the reactive measures you suggest from occurring. First, on the date of and shortly following an IPO, there is no stock available to borrow for shorting. Second, there are no put options available for purchase. At least, none that are listed, of the sort you probably have in mind. In fact, within a day or two of the LinkedIn IPO, most (all?) of the active equity traders I know were bemoaning the fact that they couldn't yet do exactly what you described i.e. buying puts, or finding shares to sell short. There was a great deal of conviction that LinkedIn shares were overpriced, but scant means available to translate that market assessment into an influence of market value. This does not mean that the Efficient Markets Hypothesis is deficient. Equilibrium is reached quickly enough, once the market is able to clear as usual. Who's to say it wasn't priced into the markets, at least to some degree? Without any information on the behaviour of holders pre-expiry, no one can know if they've been shorting the stock in advance of selling on expiry day. And with the float being such a small proportion of the total issuance, there's always the risk of sudden fluctuations picking up big momentum - which could easily explain the 7% drop on expiry day. Add into all this uncertainty, the usual risks of shorting (e.g. limited upside, unlimited downside), and the observed phenomena aren't by any means killer blows of the Efficient Market Hypothesis. That's not to say that such evidence doesn't necessarily exist - just that this isn't it. "That's the way the markets work in THEORY. In actual fact, markets are subject to ""real world"" pressures. That is, there are so many things going on in the market that the end of the ""Lined In"" lock up is just one of many. To produce the result you describe, traders would have to hold cash in reserve for this so-called ""contingency"" to buy at the end of the lock-up. In most cases, they wouldn't want to because of everything else that is going on.  To use a real world analogy, would you want to wait until the last possible moment before going to the bathroom? Or would you go now while you had the chance? That's what the decision about ""holding cash in reserve for a contingency"" is like."
You'd likely be subject to a lock-up period before you could sell the shares along with possibly having other rules about how you could sell your shares as you'd likely be seen as an insider that may have information that gives you an unfair advantage for selling the stock possibly. Depending on how far in advance you hold the shares, you may or may not have adjustments in the valuation and number of shares as some companies may do a split or reverse split when preparing for an IPO. A company I worked for in the late 1990s had an IPO and my stock options had a revised strike price because of a reverse stock split that was done prior to the IPO. If you believe in the efficient market hypothesis then the stock price reflects the information known to market participants. Consequently, if the 'market' expected earnings to rise, and they did, then the price won't change. Clearly there are circumstances, especially in the short term and for illiquid stocks, where this isn't true, but a lot of work points to this being the case on average. Markets are rational in the long term. Actors act rationally given the knowledge they have. They don't have perfect knowledge - meaning they're prone to make mistakes. However, in the LONG run, every would be a equilibrium.   Facebook stock is clearly over valued and the market is adjusting to the real price. Nothing spectacular going on there. Some brokers have a number of shares they can offer their customers, but the small guy will get 100, not as many as they'd like. In the Tech bubble of the late 90's I was able to buy in to many IPOs, but the written deal from the broker is that you could not sell for 30 days or you'd be restricted from IPO purchases for the next 90. No matter what the stock opened at, there were a fair number of stocks thay were below IPO issue price after 30 days had passed. I haven't started looking at IPOs since the tech flameout, but had I gotten in to LinkedIn it would have been at that $45 price. Let's see if it stays at these levels after 30 days.  Edit - This is the exact cut/paste from my broker's site :  Selling IPO Shares: While XXX customers are always free to sell shares purchased in a public offering at any time, short holding periods of less than 31 calendar days will be a factor in determining whether XXX allocates you shares in future public offerings. Accordingly, if you sell IPO shares purchased in a public offering within 30 calendar days of such purchase, you will be restricted from participating in initial and secondary public offerings through XXX for a period of 3 months.  (I deleted the broker name) I honestly don't know if I'd have gotten any LI shares. Next interesting one is Pandora. 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. "If the market is reasonably efficient, why wouldn't this become a self-defeating prophecy, with the eventual recovery priced in throughout the whole recession? Eventual, but when?  That is a big unknown.  In fact, even a recovery is not guaranteed.  Japan's long deleveraging process is brought up often enough with regard to our current long and painful economic downturn. Given that the business cycle isn't predictable This is one of the big issues.  If things were predictable, investing would be easy and there probably wouldn't be as much money to be made in it. owning stocks with a short time horizon is generally a bad idea Agreed.  However, it does not mean that this does not happen.  In fact, it happens every day.  It's called day trading.  Also, it is possible to make money that way, else it would not occur.  So, strictly speaking, whether it is a good or bad idea comes down to specific situations. why would anyone buy stocks in the first place if they weren't prepared to ride out a recession if one happens? These things tend to happen at the worst times and they have a way of compounding or piling-up.  E.g. you overextend yourself, the economy goes south, you find yourself jobless and unable to pay the mortgage, you are forced to liquidate some of your positions because you need cold, hard cash. Benjamin Graham is widely quoted to have stated that the stock market is a voting (opinion) machine in the short term and a weighing (fact) machine in the long term.  This may not feel very satisfying to you: but, it is just the way it is. While the dissemination of information may be relatively efficient, the interpretation of that information is quite variable.  It is not easy to put a number to most events.  (By ""put a number"" I mean determine the impact to the balance sheet.) It is a complicated system, with many inputs and many actors, which have varying goals.  While there may be an effective, Zen-like approach to investing, the markets cannot actually be simplified to ""buy low, sell high"" in practice.  Or, more specific to your question ""buy and hold"" is a simple idea, that is not necessarily easy to implement. Prompted by JoeTaxpayer's comment, I went searching for one of my favorite quotes regarding the markets: ""Markets can remain irrational a lot longer than you and I can remain solvent."" -- John Maynard Keynes And, I came across this one, which I think applies quite well to this question: ""The long run is a misleading guide to current affairs. In the long run we are all dead."" -- John Maynard Keynes" To answer your original question: There is proof out there. Here is a paper from the Federal Reserve Bank of St. Louis that might be worth a read.  It has a lot of references to other publications that might help answer your question(s) about TA.  You can probably read the whole article then research some of the other ones listed there to come up with a conclusion.  Below are some excerpts:  Abstract: This article introduces the subject of technical analysis in the foreign exchange market, with emphasis on its importance for questions of market efficiency.  “Technicians” view their craft, the study of price patterns, as exploiting traders’ psychological regularities.  The literature on technical analysis has established that simple technical trading rules on dollar exchange rates provided 15 years of positive, risk-adjusted returns during the 1970s and 80s before those returns were extinguished.  More recently, more complex and less studied rules have produced    more modest returns for a similar length of time.  Conventional explanations that rely on risk adjustment and/or central bank intervention do not plausibly justify the observed excess returns from following simple technical trading rules.  Psychological biases, however, could contribute to the profitability of these rules. We view the observed pattern of excess returns to technical trading rules as being consistent with an adaptive markets view of the world.    and  The widespread use of technical analysis in foreign exchange (and   other) markets is puzzling because it implies  that either traders are   irrationally making decisions on useless information or that past   prices contain useful  information for trading.  The latter   possibility would contradict the “efficient markets hypothesis,”   which holds that  no trading strategy should be able to generate   unusual profits on publicly available information—such as past    prices—except by bearing unusual risk. And the observed  level of   risk-adjusted profitability measures market  (in)efficiency. Therefore   much research effort has been directed toward determining whether   technical analysis is  indeed profitable or not. One of the earliest   studies, by Fama and Blume (1966), found no evidence that a particular   class of TTRs could earn abnormal profits in the stock market.   However, more recent research by Brock,  Lakonishok and LeBaron (1992)   and Sullivan, Timmermann an d White (1999) has provided contrary   evidence. And  many studies of the foreign exchange market have found   evidence that TTRs can generate persistent profits (Poole  6  (1967),   Dooley and Shafer (1984), Sweeney (1986), Levich and Thomas (1993),   Neely, Weller and Dittmar (1997),  Gençay (1999), Lee, Gleason and   Mathur (2001) and Martin (2001)). A lot can happen to a stock's price in 1 hour and especially 30 days.  Not allowing investors to back out of if they desire would be a bad idea.  These HFT firms operate on milliseconds.  Requiring investors to hold for even just 1-5 seconds would be a major blow to the industry. "This is a good question and my answer below, being the first rationale that crossed my mind, is far from fleshed-out. It's just a reply based on many books on the historical cycles of markets and it's something I've discussed at work (I work in finance).   Historically we can observe that periods of financial ""booms"" entailing high valuations of public equities tend to lead to lower returns. It's a fairly simplistic notion, but if you're paying more now for something - when it's potentially close to a high water mark - then you're returns in the short term are likely to be somewhat stunted. Returns from the underlying companies have a hard time keeping up with high valuations such that investors aren't likely to see a bountiful return in the short run." "In some respects the analysis for this question is similar to comparing a ""safe"" return on a government bond vs. holding the stock market. Typically, the stock market's expected return will be higher -- i.e., there's a positive equity risk premium -- vs. a government bond (assuming it's held to maturity). There's no guarantee that the stock market will outperform, although the probability of outperformance rises (some analysts argue) the longer the holding period for equities beyond, say, 10 years. That's why there's generally a positive equity risk premium, otherwise no one (or relatively few investors) would hold equities." "To answer your question directly..  you can investigate by using google or other means to look up research done in this area.  There's been a bunch of it Here's an example of search terms that returns a wealth of information. effect+of+periodic+rebalancing+on+portfolio+return I'd especially look for stuff that appears to be academic papers etc, and then raid the 'references' section of those.  Look for stuff published in industry journals such as ""Journal of Portfolio Management"" as an example. If you want to try out different models yourself and see what works and what doesn't, this Monte Carlo Simulator might be something you would find useful The basic theory for those that don't know is that various parts of a larger market do not usually move in perfect lockstep, but go through cycles.. one year tech might be hot, the next year it's healthcare.  Or for an international portfolio, one year korea might be doing fantastic only to slow down and have another country perform better the next year.    So the idea of re-balancing is that since these things tend to be cyclic, you can get a higher return if you sell part of a slice that is doing well (e.g. sell at the high) and invest it in one that is not (buy at the low) Because you do this based on some criteria, it helps circumvent the human tendency to 'hold on to a winner too long' (how many times have you heard someone say 'but it's doing so well, why do I want to sell now""? presuming trends will continue and they will 'lose out' on future gains, only to miss the peak and ride the thing down back into mediocrity.)  Depending on the volatility of the specific market, and the various slices, using re balancing can get you a pretty reasonable 'lift' above the market average, for relatively low risk. generally the more volatile the market, (such as say an emerging markets portfolio) the more opportunity for lift. I looked into this myself a number of years back, the concensus I came was that the most effective method was to rebalance based on 'need' rather than time.  Need is defined as one or more of the 'slices' in your portfolio being more than 8% above or below the average.  So you use that as the trigger. How you rebalance depends to some degree on if the portfolio is taxable or not.  If in a tax deferred account, you can simply sell off whatever is above baseline and use it to buy up the stuff that is below.   If you are subject to taxes and don't want to trigger any short term gains, then you may have to be more careful in terms of what you sell.  Alternatively if you are adding funds to the portfolio, you can alter how your distribute the new money coming into the portfolio in order to bring up whatever is below the baseline (which takes a bit more time, but incurs no tax hit)  The other question is how will you slice a given market?  by company size?  by 'sectors' such as tech/finance/industrial/healthcare, by geographic regions?" There has been a lot of research on the effects of stock splits. Some studies have concluded that: However note that (i) these are averages over large samples and does not say it will work on every split and (ii) most of the research is a bit dated and more recent papers have often struggled to find any significant performance impact after 1990, possibly because the effect has been well documented and the arbitrage no longer exists. This document summarises the existing research on the subject although it seems to miss some of the more recent papers. More practically, if you pay a commission per share, you will pay more commissions after the split than before. Bottom line: don't overthink it and focus on other criteria to decide when/whether to invest. Not sure of the question here if by IPO(initial public offering) you mean private company then:  A company can invest its excess money into other companies, to earn returns.  Also a company that is private can attract private investment if the sector is doing well on publicly traded markets.  Finally a company can diversify away risk, by holding shares of a company that would benefit in the event of a disruption in their own industry. "No, but it is certainly a possibility. the efficient market hypothesis would say that this means that the market perceives the present value of all future earning as negative. These earnings might take the form of a writedown of assets at some point. (Companies carry a goodwill asset that is generally imaginary.  They book that asset when they buy companies for more than they are worth.) It would be as if PRUN was a stock tracking my life.  If I bought my house in 2006 for $1 million cash. I might have a book value of $1 million.  However, PRUN might trade at $500k because the market knows that my asset isn't really worth $1 million and at some point my earnings will take a hit to reflect that. It might also mean that future ""real"" earnings ""ie actual profit and loss on sales"" are going to be negative. This would mean bankruptcy is more likely." "This was an article meant for mass consumption, written by a Yale law professor and an individual who has a PhD in economics (in addition to his practical, on the job experience managing the Yale endowment).  I'm having a hard time believing that it was ""poorly argued.""  As for proof, that's the sort of thing you find in financial and economic journals (for example, [The Effect of Maker-Taker Fees on Investor Order Choice and Execution Quality in U.S. Stock Markets](http://people.stern.nyu.edu/jhasbrou/SternMicroMtg/SternMicroMtg2015/Papers/MakerTakerODonoghue.pdf)).    One of the direct takeaways from the above paper states:  *""I find that total trading cost to investors increases, when the taker fee and maker rebate increase, even if the net fee is held fixed. The total trading cost represents the net-of-fees bid-ask spread and the brokerage commission to an investor wanting to buy and then sell the same stock.""*  I'm not here to argue for the paper.  I'm really here to tell you that these guys have far more of a clue than you realize.  ~~A dash of humility on your part may be in order, given the fact that you've already admitted to the reality that you aren't sure of any of this yourself.~~  *Edit*:  Thought I was responding to a different thread."