The Efficient Market Hypothesis: Theory, Evidence, and Implications

8.1 RANDOM WALKS AND THE EFFICIENT MARKET HYPOTHESIS CHAPTER 8 The Efficient Market Hypothesis Efficient Market Hypothesis (EMH) Do security prices reflect information Why look at market efficiency – Implications for business and corporate finance – Implications for investment Random Walk with Positive Trend Security Prices Random Walk and the EMH Random Walk - stock prices are random – Randomly evolving stock prices are the consequence of intelligent investors competing to discover relevant information Expected price is positive over time Positive trend and random about the trend Random Price Changes Why are price changes random – Prices react to information – Flow of information is random – Therefore, price changes are random Time 8-1 Figure 8.1 Cumulative Abnormal Returns Before Takeover Attempts Figure 8.2 Stock Price Reaction to CNBC Reports EMH and Competition Versions of the EMH Stock prices fully and accurately reflect publicly available information Once information becomes available, market participants analyze it Competition assures prices reflect information Weak SemiSemi-strong Strong Types of Stock Analysis 8.2 IMPLICATIONS OF THE EMH Technical Analysis - using prices and volume information to predict future prices – Weak form efficiency & technical analysis Fundamental Analysis - using economic and accounting information to predict stock prices – Semi strong form efficiency & fundamental analysis 8-2 Implications of Efficiency for Active or Passive Management Active Management – Security analysis – Timing Passive Management – Buy and Hold – Index Funds The Role of Portfolio Management in an Efficient Market Even if the market is efficient a role exists for portfolio management: – Appropriate risk level – Tax considerations – Other considerations Empirical Tests of Market Efficiency 8.3 ARE MARKETS EFFICIENT Magnitude Issue – Actions of intelligent investment managers are the driving force Selection Bias Issue – The outcomes we observe have been preselected in favor of failed attempts – Cannot evaluate the true ability of portfolio managers Lucky Event Issue Weak-Form Tests: Patterns in Stock Returns Returns over short horizons – Very short time horizons small magnitude of positive trends – 3-12 month some evidence of positive momentum Returns over long horizons – pronounced negative correlation Evidence on Reversals Predictors of Broad Market Returns Fama and French – Aggregate returns are higher with higher dividend ratios Campbell and Shiller – Earnings yield can predict market returns Keim and Stambaugh – Bond spreads can predict market returns 8-3 Semi-Strong Tests: Market Anomalies P/E Effect Small Firm Effect (January Effect) Figure 8.3 Returns in Excess of RiskFree Rate and in Excess of the SML – Invest in lowlow-capitalization stocks – Earn excess returns Semi-Strong Tests: Market Anomalies (Con’t) Neglected Firm Figure 8.4 Average Annual Return as a Function of Book-to-Market – Small firms tend to be neglected by large institutional traders BookBook-toto-Market Ratios – Beta seems to have no power to explain average security returns Semi-Strong Tests: Market Anomalies (Con’t) Figure 8.5 Cumulative Abnormal Returns in Response to Earnings Announcements PostPost-Earnings Announcement Drift – There is a large abnormal return on the earnings announcement day 8-4 Strong-Form Tests: Inside Information Interpreting the Evidence The ability of insiders to trade profitability in their own stock has been documented in studies by Jaffe, Seyhun, Givoly, and Palmon SEC requires all insiders to register their trading activity Risk Premiums or market inefficiencies— inefficiencies— disagreement here Figure 8.6 Return to Style Portfolio as a Predictor of GDP Growth Interpreting the Evidence (Con’t) – Fama and French argue that these effects can be explained as manifestations of risk stocks with higher betas – Lakonishok, Shleifer, and Vishney argue that these effects are evidence of inefficient markets Anomalies or Data Mining – Rerun the computer database of past returns over and over and examine stock returns along enough dimensions: Simple chance may cause some criteria to appear to predict returns Stock Market Analysts 8.4 MUTUAL FUND AND ANALYST PERFORMANCE Do analysts add value— value—mixed evidence – Womack study found that positive changes are associated with increased stock prices of about 5% – Negative changes result in average price decreases of 11% – Are prices change due to analysts’ analysts’ information or through pressure brought on by the recommendations themselves 8-5 Mutual Fund Managers Some evidence of persistent positive and negative performance Potential measurement error for benchmark returns Figure 8.7 Estimates of Individual Mutual Fund Alphas – Style changes – May be risk premiums Superstar phenomenon Table 8.1 Performance of Mutual Funds Based on Three-Index Model Figure 8.8 Persistence of Mutual Fund Performance Table 8.2 Two-Way Table of Managers Classified by Risk-Adjusted Returns over Successive Intervals 8-6