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Market Efficiency in an Irrational World

  • Kent Daniel
  • Sheridan Titman

This paper explains why investors are likely to be overconfident and how this behavioral bias affects investment decisions. Our analysis suggests that investor overconfidence can potentially generate stock return momentum and that this momentum effect is likely to be the strongest in those stocks whose valuation requires the interpretation of ambiguous information. Consistent with this, we find that momentum effects are stronger for growth stocks than value stocks. A portfolio strategy based on this hypothesis generates strong abnormal returns that do not appear to be attributable to risk. Although these results violate the traditional efficient markets hypothesis, they do not necessarily imply that rational but uniformed investors, without the benefit of hindsight, could have actually achieved the returns. We argue that to examine whether unexploited profit opportunities exist, one must test for what we call adaptive-efficiency, which is a somewhat weaker form of market efficiency that allows for the appearance of profit opportunities in historical data, but requires these profit opportunities to dissipate when they become apparent. Our tests reject this notion of adaptive-efficiency.

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File URL: http://www.nber.org/papers/w7489.pdf
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Paper provided by National Bureau of Economic Research, Inc in its series NBER Working Papers with number 7489.

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Date of creation: Jan 2000
Date of revision:
Publication status: published as Financial Analyst Journal (1999).
Handle: RePEc:nbr:nberwo:7489
Note: AP
Contact details of provider: Postal: National Bureau of Economic Research, 1050 Massachusetts Avenue Cambridge, MA 02138, U.S.A.
Phone: 617-868-3900
Web page: http://www.nber.org
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  1. Lars Peter Hansen & Ravi Jagannathan, 1990. "Implications of Security Market Data for Models of Dynamic Economies," NBER Technical Working Papers 0089, National Bureau of Economic Research, Inc.
  2. Andrei Shleifer & Robert W. Vishny, 1995. "The Limits of Arbitrage," NBER Working Papers 5167, National Bureau of Economic Research, Inc.
  3. Harrison Hong & Jeremy C. Stein, 1999. "A Unified Theory of Underreaction, Momentum Trading, and Overreaction in Asset Markets," Journal of Finance, American Finance Association, vol. 54(6), pages 2143-2184, December.
  4. Kent Daniel & David Hirshleifer & Avanidhar Subrahmanyam, 1998. "Investor Psychology and Security Market Under- and Overreactions," Journal of Finance, American Finance Association, vol. 53(6), pages 1839-1885, December.
  5. Waldman, Michael, 1994. "Systematic Errors and the Theory of Natural Selection," American Economic Review, American Economic Association, vol. 84(3), pages 482-97, June.
  6. Grossman, Sanford J & Stiglitz, Joseph E, 1980. "On the Impossibility of Informationally Efficient Markets," American Economic Review, American Economic Association, vol. 70(3), pages 393-408, June.
  7. Harrison Hong & Terence Lim & Jeremy C. Stein, 2000. "Bad News Travels Slowly: Size, Analyst Coverage, and the Profitability of Momentum Strategies," Journal of Finance, American Finance Association, vol. 55(1), pages 265-295, 02.
  8. Barberis, Nicholas & Shleifer, Andrei & Vishny, Robert, 1998. "A model of investor sentiment," Journal of Financial Economics, Elsevier, vol. 49(3), pages 307-343, September.
  9. Gervais, Simon & Odean, Terrance, 2001. "Learning to be Overconfident," Review of Financial Studies, Society for Financial Studies, vol. 14(1), pages 1-27.
  10. J. Bradford De Long & Andrei Shleifer & Lawrence H. Summers & Robert J. Waldmann, 1988. "The Survival of Noise Traders in Financial Markets," NBER Working Papers 2715, National Bureau of Economic Research, Inc.
  11. Merton, Robert C, 1987. " A Simple Model of Capital Market Equilibrium with Incomplete Information," Journal of Finance, American Finance Association, vol. 42(3), pages 483-510, July.
  12. Carhart, Mark M, 1997. " On Persistence in Mutual Fund Performance," Journal of Finance, American Finance Association, vol. 52(1), pages 57-82, March.
  13. Lo, Andrew W & MacKinlay, A Craig, 1990. "When Are Contrarian Profits Due to Stock Market Overreaction?," Review of Financial Studies, Society for Financial Studies, vol. 3(2), pages 175-205.
  14. Shmuel Kandel & Robert F. Stambaugh, 1995. "On the Predictability of Stock Returns: An Asset-Allocation Perspective," NBER Working Papers 4997, National Bureau of Economic Research, Inc.
  15. K. Geert Rouwenhorst, 1998. "International Momentum Strategies," Journal of Finance, American Finance Association, vol. 53(1), pages 267-284, 02.
  16. Chan, Louis K C & Jegadeesh, Narasimhan & Lakonishok, Josef, 1996. " Momentum Strategies," Journal of Finance, American Finance Association, vol. 51(5), pages 1681-1713, December.
  17. Fama, Eugene F. & French, Kenneth R., 1993. "Common risk factors in the returns on stocks and bonds," Journal of Financial Economics, Elsevier, vol. 33(1), pages 3-56, February.
  18. Daniel, Kent, et al, 1997. " Measuring Mutual Fund Performance with Characteristic-Based Benchmarks," Journal of Finance, American Finance Association, vol. 52(3), pages 1035-58, July.
  19. Terrance Odean, 1998. "Are Investors Reluctant to Realize Their Losses?," Journal of Finance, American Finance Association, vol. 53(5), pages 1775-1798, October.
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