Efficient Market Hypothesis The concepts

Efficient Market HypothesisThe concepts

Topics • What if you figure a stock price moving pattern? • Some formal definitions • Implications of Efficient Market Hypothesis • Price modeling • Empirical studies What if? Definitions Implications Price Empirics

What if • What if you have figured out the following: • Buy if out of the 20 trading days for the past month, stock XYZ has been rising for more than 10%. • Sell if out of the 20 trading days for the past month, stock XYZ has been falling for more than 10%. • Follow this rule strictly, return is “abnormally high”. What if? Definitions Implications Price Empirics

Stock price reflects information • If you have spotted such price pattern that seems to guarantee you a sure profit, what should you do? • You should definitely exploit it. (How? Borrow as much as you can to invest according to your strategy.) • The process of exploiting the pattern actually ironically destroy the pattern because: • You would bid up XYZ share price when you think it is hot. ↑ Price => ↓ Expected[Return] • You would bid down XYZ share price when you think it is cold. ↓ Price => ↑ Expected[Return] • The fact that you have figured out a stock price movement is very likely to be reflected by the stock price. • The more greedy (which is rational. More precisely, is the higher the ability for you to raise fund) you are, the faster your pattern will be eliminated by your own hands. • Bottom line: info, private or public, is reflected in stock prices. What if? Definitions Implications Price Empirics

Sell Sell Buy Buy Price movement pattern Investors’ behaviors tend to eliminate any profit opportunity associated with stock price patterns. Stock Price If it were possible to make big money simply by finding “the pattern” in the stock price movements, everyone would have done it and the profits would be competed away. Time What if? Definitions Implications Price Empirics

The army • If you are one of the stock hunters, actively looking for price patterns, who are you competing with? What if? Definitions Implications Price Empirics

The army • Imagine not only you, there is essentially an “army” of intelligent, well-informed security analysts, traders, who literally spend their lives hunting for mis-priced securities or securities that follow a pattern based on currently available information. • They have high-tech computers, subscription to professional database, up-to-date information on thousands of firms, state-of-the-art analytical technique, etc. • These people can assess, assimilate and act on information, very quickly. • In their intense search for mis-priced securities, professional investors may “police” the market so efficiently that they drive the prices of all assets to fully reflect all available information. What if? Definitions Implications Price Empirics

Implications • Competition for finding mis-priced securities is fierce. • Such competition always kills the “sure-profit” pattern. Were there one, it would have been exploited by someone who first spotted it. Thus, roughly speaking, “no arbitrage” should hold. • The first one does make abnormal profit, but Economic profit ≠ gross profit • The “very first” one is not likely to be you. • Even if you are the “very first” one, you are likely to pay higher brokerage and commission fees than institutional investors. • The implications: • stock prices should have reflected all available information. • stock prices should be unpredictable. What if? Definitions Implications Price Empirics

Unpredictability • Prices are unpredictable in the sense that stock prices should have reflected “all available information”. • Thus if stock prices change, it should be reacting only to “new information”. • The fact that information is new means stock prices are unpredictable. What if? Definitions Implications Price Empirics

Market efficiency • If all past information is incorporated in the price then it should be impossible to consistently beat the market using technical analysis and the like. • Definition 1: • Eugene Fama defined Market Efficiency as the state where "security prices reflect all available information.“ • Definition 2: • Financial markets are efficient if current asset prices fully reflect all currently available relevant information. What if? Definitions Implications Price Empirics

The right question to ask • If new information becomes known about a particular company, how quickly do market participants find out about the information and buy or sell the securities of the company based on the information? • How quickly do the prices of the securities adjust to reflect the new information? • The issue is not merely black or white. We know that the market should neither be strictly efficient nor strictly inefficient. The question is one of degree. • We should ask “ how efficient the market really is?” What if? Definitions Implications Price Empirics

Subsets of available informationFor a given stock All Available Information including inside or private information All Public Information Information in past stock prices What if? Definitions Implications Price Empirics

3 forms of market efficiency hypothesis Since we are more interested in how efficient is the capital market, we define the following 3 forms of market efficiency hypothesis: “A market is efficient if it reflects ALL available information” [1] Strong-form - ALL available info [2] Semi-strong form - ALL available info [3] Weak-form - ALL available info All Available Information including inside or private information All Public Information Information in past stock prices What if? Definitions Implications Price Empirics

3 forms of market efficiency hypothesis • Weak-form “Stock prices are assumed to reflect any information that may be contained in the past stock prices.” • For example, suppose there exists a seasonal pattern in stock prices such that stock prices fall on the last trading day of the year and then rise on the first trading day of the following year. Under the weak-form of the hypothesis, the market will come to recognize this and price the phenomenon away. • Anticipating the rise in price on the first day of the year, traders will attempt to get in at the very start of trading on the first day. Their attempts to get in will cause the increase in price to occur in the first few minutes of the first day. Intelligent traders will then recognize that to beat the rest of the market, they will have to get in late on the last day. The consequences, therefore, is the elimination of the pattern as price in the last trading day should be bid up. What if? Definitions Implications Price Empirics

3 forms of market efficiency hypothesis • Semi-strong-form “Stock prices are assumed to reflect any information that is publicly available.” • These include information on the stock price series, as well as information in the firm’s accounting reports, the past prices and reports of competing firms, announced information relating to the state of the economy, and any other publicly available information relevant to the valuation of the firm. What if? Definitions Implications Price Empirics

3 forms of market efficiency hypothesis • Strong-form “Stock prices are assumed to reflect ALL information, regardless of them being public or private.” • Under this form, those who acquire insider information act on it, buying or selling the stock. Their actions affect the price of the stock, and the price quickly adjusts to reflect the insider information. What if? Definitions Implications Price Empirics

3 forms of market efficiency hypothesis • If Weak-form of the hypothesis is valid: • Technical analysis or charting becomes ineffective. You won’t be able to gain abnormal returns based on it. • If Semi-strong form of the hypothesis is valid: • No analysis will help you attain abnormal returns as long as the analysis is based on publicly available information. • If Strong-form of the hypothesis is valid: • Any effort to seek out insider information to beat the market are ineffective because the price has already reflected the insider information. Under this form of the hypothesis, the professional investor truly has a zero market value because no form of search or processing of information will consistently produce abnormal returns.(Even if Steve Jobs is your uncle, you can’t profit from listening to his phone calls and trading APPLE stocks.) What if? Definitions Implications Price Empirics

Why do we care about capital market efficiency? • As an analyst • As an investment manager • As a corporate financial manager • As a marketing manager • As an accounting manager What if? Definitions Implications Price Empirics

Why do we care about capital market efficiency? • As an analyst • If market is efficient, what is your marginal contribution for your securities firm? It should be zero, because you will not be able to spot mis-priced securities to produce additional returns on the portfolios that you are managing. Heat Debate. • Analysts’ total contribution to the society should be big. Because in scouting the capital market, they essentially make sure asset prices are effective as signals to others. • If the market is truly efficient => 0<Total contribution ≠ marginal contribution=0 What if? Definitions Implications Price Empirics

Why do we care about capital market efficiency? • As an investment manager • Investment decisions of the managers of any firms are based to a large extent on signals they get from the capital market. • If the market is efficient, the cost of acquiring capital will accurately reflect the prospects for each project. • This means the firms with the most attractive investment opportunities will be able to obtain capital at a fair price which reflects their true potentials. • The “right” investment will be made, and the society is said to be “allocationally-efficient”. Everyone’s better off. What if? Definitions Implications Price Empirics

Why do we care about capital market efficiency? • As a corporate financial manager • To raise capital, you consider getting debt- or equity-financing. (Corporate Finance) • If the market is efficient, you know that equity-financing requires a rate of return which is “fair” because the price has already reflected all available information. • If the market is efficient, you would never feel your firm’s stock being under- or over-valued at any point in time. In essence, there is no timing decision to issuing equity. • More profoundly, if market is efficient, every alternative way of raising capital would require the same rate of return for the same project. And no one capital-raising method is superior than the other. What if? Definitions Implications Price Empirics

Why do we care about capital market efficiency? • As a marketing manager • You may consider advertising at the Wall Street Journal about how impressive your company has be doing in the past few years. • If the market is efficient, there is no need to do that. Because your stock price has already reflected those. There is absolutely no impact for the ad on the stock price. And placing an ad is like burning money. • A more sensible interpretation is that, “ads don’t easily fool investors.” What if? Definitions Implications Price Empirics

Why do we care about capital market efficiency? • As an accounting manager • Will change in accounting practices (e.g., different depreciation methods: straight-line vs accelerated) impact the company’s stock price? • No if the market is semi-strong efficient. Because informed, rational analysts will adjust the different accounting procedures used by different firms and assess prospects based on standardized numbers. • Thus, the adjustment in accounting technique will have no effect on the opinions of those analysts or on the stock price of the firm. What if? Definitions Implications Price Empirics

Expected return-risk • The Efficient Market Hypothesis imposes no structure on stock prices. However, what is abnormal return? Abnormal return = Actual return – Expected return • This means we have to know what exactly is expected return. • That’s why we may rely on an asset pricing model. • e.g.,CAPM, to find a risk-adjusted return that the market will be rewarding.) • Defining abnormal return inherently involves assuming a pricing model. If we find abnormal returns, we conclude that the market is inefficient. But then, we can also say that the pricing model we used is invalid. • The challenge here is: testing market efficiency inevitably involves testing a joint hypothesis: • H0 : both market is efficient and the pricing model is valid. • H1 : EITHER market is inefficient OR the pricing model is invalid. What if? Definitions Implications Price Empirics

4 basic traits of efficiency • An efficient market exhibits certain behavioral traits. We can examine the real market to see if it conforms to these traits. If it doesn’t, we can conclude that the market is inefficient. • Act to new information quickly and accurately • Price movement is unpredictable (memory-less) • No trading strategy consistently beat the market • Investment professionals not that professional What if? Definitions Implications Price Empirics

1) Act to news quickly & accurately Stock price ($) Days relative to announcement day -t 0 +t The timing for a positive news What if? Definitions Implications Price Empirics

1) Act to news quickly & accurately Stock price ($) Days relative to announcement day -t 0 +t If the market is efficient, 1) at time 0, the positive news come, there is an immediate jump of the share price to the RIGHT level. (i.e., the PINK path) 2) There is no delays in analyzing news and slowly reflecting in the share price like the ORANGE path does. 3) There is also no over-reaction like the BLUE path does, and then subsequently adjustment back to the correct level. What if? Definitions Implications Price Empirics

2) Memory-less price movement • If the market is efficient (WEAK-FORM), • The so-called “momentum” is nothing. (Google “Stock momentum”) • “momentum” is like, if once started on a downward slide, stock prices develop a propensity to continue sliding. The expected change in today’s price would, in fact, be related (correlated positively) with the price changes in the past. • 2) If the market is efficient, prices only move in response to “news”. More precisely, “news” is any discrepancy between the public’s expectation and the actual realized event. E.g, “Suppose everyone expects RIM’s sales should have gone up by 30%. If RIM does announce that its sales has gone up by 30%, it is not a news. If it has gone up by 29% instead, it is a news, a negative one though.” • 3) To detect “memory” or “momentum”, we try to see if • Cov(ΔPt, ΔPt-i) is significantly different from zero or not, for i ≠ 0 What if? Definitions Implications Price Empirics

3) No superior trading strategies • One way to test for market efficiency is to test whether a specific trading rule or investment strategy, would have CONSISTENTLY produced abnormally high return. • Problem about such test is: • What is abnormal return again? We run into the problem of joint hypothesis testing again in order to find an expected return as benchmark. • What kind of information you use to construct an investment strategy? Can you be sure the information you are based on really reflect what WAS available when the decision to invest was made. • E.g., Last quarter’s earning is out around February of next year. If a WINNING investment strategy says “invest in the top 10 companies last year by Jan”, it is not an employable strategy. • What is the cost of implementing a strategy? What if? Definitions Implications Price Empirics

4) Professionals aren’t that professional • If professional investors consistently beat the market, we conclude that the market is not that efficient. • If the market is really efficient, we should not see professionals making abnormally high returns. • The puzzle is: “we do see professionals, like Peter Lynch and Warren Buffet, having amazing records.” • A defense, a weak one though, is: • “Suppose we take a thousand people in a gigantic stadium. Have them flip coins. Suppose “head” is winning and “tail” is losing. There is no surprise to find a few individual “flippers” with unbelievable records of success and failure. Those having 20 heads in a row goes on TV and showcase their exceptional flipping skills. But we know they’re just plain lucky.” What if? Definitions Implications Price Empirics

So what’s the value for portfolio management • If capital markets are efficient, should we just throw darts at the financial page to pick stocks instead of spending time carefully construct a stock portfolio? • The answer is 3 NO NO NO. • As you have learnt, you need to have a well-diversified portfolio that is tailored towards your risk-preference. • Depending on your age, your risk-preference, your current situation, your tax bracket, and all other relevant factors, your portfolio should be carefully constructed. • Don’t forget that there is value for diversification. There is value for you to learn options. There is value for you to tailor a future payoff profile specific to your own needs. Throwing darts to pick stocks does not guarantee your specific needs are met. What if? Definitions Implications Price Empirics

So what’s the value for portfolio management • The conclusion is: • capital market is neither purely efficient nor purely inefficient. • The right question to ask is “the degree of efficiency of capital market.” • The more efficient capital market is, the better off the society. • But even if it is efficient, it doesn’t imply knowledge of finance is useless. Because you have learnt diversification and portfolio theory that is based on maximizing happiness. • Price movements are random. But it in NO way implies prices are random. Prices reflect/incorporate available information. The driving force to their random movements is that news comes randomly. What if? Definitions Implications Price Empirics

Efficient Market Hypothesis The concepts