Empirical Challenges of the Efficient Market Hypothesis
Empirical Challenges to the Efficient Market Hypothesis
1. Introduction
Random walks observed in stock return series prior to the 1970s puzzled a number of financial theorists and practitioners. In 1970, this puzzle was resolved by Eugene Fama (1970) who argued that the random walks observed in the behaviour of stock return series could be attributed to market efficiency. Market efficient meant that investors could not consistently make risk-adjusted returns by making investment decisions that were based solely on past stock market information. This is because; the information was already reflected in the stock price. Following its initial proposition, the efficient market hypothesis has remained one of the most important topics of debate in the financial and economic literature. This paper provides a discussion of the empirical challenges of the hypothesis.
2. Efficient Market Hypothesis: Theory and Empirical Challenges
There are three forms of the efficient market hypothesis: (i) the weak-form; (ii) the semi strong-from; and (iii) the strong-form (Fama, 1970, 1991). The weak-form suggests that asset prices already reflect all stock market information meaning that stock market information cannot be used to make abnormal returns on a risk-adjusted based. The semi strong-from suggests that in addition to stock market information, stock prices also reflect all publicly available information such as price-to-book ratios, dividend yield, price-to-cash flow and price-to-earnings ratios. The semi strong-form means that abnormal returns cannot be made by trading on stock market data and any other information that is disclosed to the general public about stocks (Reilly and Brown, 2009). Finally, the strong-form states that security prices reflect both public and private information (Reilly and Brown, 2009).
The empirical evidence on the efficient market hypothesis is mixed. Some studies have showed that the efficient market hypothesis is
1. Introduction
Random walks observed in stock return series prior to the 1970s puzzled a number of financial theorists and practitioners. In 1970, this puzzle was resolved by Eugene Fama (1970) who argued that the random walks observed in the behaviour of stock return series could be attributed to market efficiency. Market efficient meant that investors could not consistently make risk-adjusted returns by making investment decisions that were based solely on past stock market information. This is because; the information was already reflected in the stock price. Following its initial proposition, the efficient market hypothesis has remained one of the most important topics of debate in the financial and economic literature. This paper provides a discussion of the empirical challenges of the hypothesis.
2. Efficient Market Hypothesis: Theory and Empirical Challenges
There are three forms of the efficient market hypothesis: (i) the weak-form; (ii) the semi strong-from; and (iii) the strong-form (Fama, 1970, 1991). The weak-form suggests that asset prices already reflect all stock market information meaning that stock market information cannot be used to make abnormal returns on a risk-adjusted based. The semi strong-from suggests that in addition to stock market information, stock prices also reflect all publicly available information such as price-to-book ratios, dividend yield, price-to-cash flow and price-to-earnings ratios. The semi strong-form means that abnormal returns cannot be made by trading on stock market data and any other information that is disclosed to the general public about stocks (Reilly and Brown, 2009). Finally, the strong-form states that security prices reflect both public and private information (Reilly and Brown, 2009).
The empirical evidence on the efficient market hypothesis is mixed. Some studies have showed that the efficient market hypothesis is
References: Balaban, E. (1995). Informational efficiency of the Istanbul Securities Exchange and some rationale for public regulation. Research paper in banking and finance. UK: Institute of European Finance. Banz, R. W. (1981), “The relationship between return and market value of common stock”, Journal of Financial Economics, vol. 9, pp. 3-18. Barberies N., Shleifer A., Vishny R. (1998). “A model of investor sentiment”, Journal of Financial Economics, vol. 49, pp 307-343. Barberies, N., Thaler, R. (2003), “A Survey of Behavioral Finance”, Handbook of the Economics of Finance, Edited by G.M. Constantinides, M. Harris and R. Stulz, Elsevier Science. Bodie, Z., Kane, A., Marcus, A. J. (2007), Investments, Seventh Edition, McGraw-Hill D’Ambrosio, C DeBondt, W., Thaler, R. (1985). “Does the stock market overreact?”, Journal of Finance, 40, 793-805. Fama, E. F. (1991) “Efficient Capital Markets: II”, Journal of Finance, 46, 5, p1575-1617. Fama, E. F. (1998) “Market Efficiency, Long-term returns, and behavioural finance”, Journal of Financial Economics, 49, 283-306. Fama, E., French, K., (1993). “Common risk factors in the returns on stocks and bonds”, Journal of Financial Economics, 33, 3-56. Fama, E., French, K., 1996. “Multifactor explanations of asset pricing anomalies”, Journal of Finance, 51, 55-84. Harvey, C. (1993). “Portfolio investment using emerging markets and conditioning information. Washington, DC: World Bank. Working paper. Hong H., Stein J.C. (1999). “A Unified Theory of Undereaction, Momentum Trading, and Overreaction in Asset Markets”, Journal of Finance, 6, 2143-2184 Jegadeesh N., Titman S Jensen, M. C. (1968) “The Performance Of Mutual Funds In The Period 1945-1964”, Harvard Business School.s Kawakatsu, H., & Morey, M Lintner, J. (1965). "The Valuation of Risk Assets and the Selection of Risky Investments in Stock Portfolios and Capital Budgets." Review of Economics and Statistics 47: pp 13-37. Lo, A. W., & MacKinlay, A. C. (1988). “Stock market prices do not follow random walks: Evidence from a simple specification test”, Review of Financial Studies, 1, 41–66. Mookerjee, R., Yu, Q (1999) “An empirical analysis of the equity markets in China”, Review of Financial Economics, 8, 41–60 Niederhoffer, V., & Osborne, M Poterba, J. M., & Summers, L. H. (1988). “Mean reversion in stock prices: Evidence and implications”, Journal of Financial Economics, 22, 27–59. Reilly, F. K., Brown, K. C (2009) “Efficient Capital Markets”, in Equity and Fixed Income, CFA Program Curriculum, vol. 5, Pearson Custom Publishing. Reinganum, M. R. (1981), “Misspecification of capital asset pricing: Empirical anomalies based on earnings yields and market values”, Journal of Financial Economics, 9, pp. 19-46. Rubinstein, M. (2001), “Rational Markets: Yes or No? The Affirmative Case”, Financial Analysts Journal, 57, 3, 15-29 Schwert G Sharpe, W. F. (1964). "Capital Asset Prices: A Theory of Market Equilibrium under Conditions of Risk." Journal of Finance, 19, 425-442.