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Herd Behavior in Efficient Financial Markets


  • Andreas Park
  • Hamid Sabourian


Rational herd behavior and informationally efficient security prices have long been considered to be mutually exclusive but for exceptional cases. In this paper we describe conditions on the underlying information structure that are necessary and sufficient for informational herding. Employing a standard sequential security trading model, we argue that people may be subject to herding if and only if there is sufficient amount of noise and, loosely, their information leads them to believe that extreme outcomes are more likely than moderate ones. We then show that herding has a significant effect on prices: prices can move substantially during herding and they become more volatile than if there were no herding. Furthermore, herding can be persistent and can affect the process of learning. We also characterize conditions for contrarian behavior. Our analysis suggests that herding (and contrarian behavior) may be more pervasive than was originally thought. Hence, the paper provides a new perspective on herding in financial markets with efficient prices

Suggested Citation

  • Andreas Park & Hamid Sabourian, 2006. "Herd Behavior in Efficient Financial Markets," Working Papers tecipa-249, University of Toronto, Department of Economics.
  • Handle: RePEc:tor:tecipa:tecipa-249

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    References listed on IDEAS

    1. Lones Smith & Peter Sorensen, 2000. "Pathological Outcomes of Observational Learning," Econometrica, Econometric Society, vol. 68(2), pages 371-398, March.
    2. Mathias Drehmann & Jörg Oechssler & Andreas Roider, 2005. "Herding and Contrarian Behavior in Financial Markets: An Internet Experiment," American Economic Review, American Economic Association, vol. 95(5), pages 1403-1426, December.
    3. Cipriani Marco & Guarino Antonio, 2008. "Herd Behavior and Contagion in Financial Markets," The B.E. Journal of Theoretical Economics, De Gruyter, vol. 8(1), pages 1-56, October.
    4. Marco Cipriani & Antonio Guarino, 2005. "Herd Behavior in a Laboratory Financial Market," American Economic Review, American Economic Association, vol. 95(5), pages 1427-1443, December.
    5. Chari, V. V. & Kehoe, Patrick J., 2004. "Financial crises as herds: overturning the critiques," Journal of Economic Theory, Elsevier, vol. 119(1), pages 128-150, November.
    6. Avery, Christopher & Zemsky, Peter, 1998. "Multidimensional Uncertainty and Herd Behavior in Financial Markets," American Economic Review, American Economic Association, vol. 88(4), pages 724-748, September.
    7. David Hirshleifer & Siew Hong Teoh, 2003. "Herd Behaviour and Cascading in Capital Markets: a Review and Synthesis," European Financial Management, European Financial Management Association, vol. 9(1), pages 25-66.
    8. Glosten, Lawrence R. & Milgrom, Paul R., 1985. "Bid, ask and transaction prices in a specialist market with heterogeneously informed traders," Journal of Financial Economics, Elsevier, vol. 14(1), pages 71-100, March.
    9. Brunnermeier, Markus K., 2001. "Asset Pricing under Asymmetric Information: Bubbles, Crashes, Technical Analysis, and Herding," OUP Catalogue, Oxford University Press, number 9780198296980, June.
    10. Paul R. Milgrom, 1981. "Good News and Bad News: Representation Theorems and Applications," Bell Journal of Economics, The RAND Corporation, vol. 12(2), pages 380-391, Autumn.
    11. Sunil Sharma & Sushil Bikhchandani, 2000. "Herd Behavior in Financial Markets; A Review," IMF Working Papers 00/48, International Monetary Fund.
    12. Abhijit V. Banerjee, 1992. "A Simple Model of Herd Behavior," The Quarterly Journal of Economics, Oxford University Press, vol. 107(3), pages 797-817.
    13. Dasgupta, Amil & Prat, Andrea, 2005. "Asset Price Dynamics When Traders Care About Reputation," CEPR Discussion Papers 5372, C.E.P.R. Discussion Papers.
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    Cited by:

    1. Marco Cipriani & Antonio Guarino, 2009. "Herd Behavior in Financial Markets: An Experiment with Financial Market Professionals," Journal of the European Economic Association, MIT Press, vol. 7(1), pages 206-233, March.
    2. Dasgupta, Amil & Prat, Andrea, 2008. "Information aggregation in financial markets with career concerns," Journal of Economic Theory, Elsevier, vol. 143(1), pages 83-113, November.
    3. Heidhues, Paul & Melissas, Nicolas, 2012. "Rational exuberance," European Economic Review, Elsevier, vol. 56(6), pages 1220-1240.

    More about this item


    Microstructure; Sequential Trades; Herding; Monotone Likelihood;

    JEL classification:

    • C70 - Mathematical and Quantitative Methods - - Game Theory and Bargaining Theory - - - General
    • D80 - Microeconomics - - Information, Knowledge, and Uncertainty - - - General
    • D83 - Microeconomics - - Information, Knowledge, and Uncertainty - - - Search; Learning; Information and Knowledge; Communication; Belief; Unawareness
    • D84 - Microeconomics - - Information, Knowledge, and Uncertainty - - - Expectations; Speculations
    • G12 - Financial Economics - - General Financial Markets - - - Asset Pricing; Trading Volume; Bond Interest Rates
    • G14 - Financial Economics - - General Financial Markets - - - Information and Market Efficiency; Event Studies; Insider Trading

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