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Why Do Individual Investors Hold Under-Diversified Portfolios?



    () (Yale School of Management - International Center for Finance)


    () (University of Notre Dame - Department of Finance)


This study examines the diversification decisions of more than 60,000 individual investors during a six year period (1991-96) in recent U.S. capital market history. The majority of investors in our sample are under-diversified and the extent of under-diversification is more severe in retirement accounts. Investors' personal characteristics, their stock preferences, and their behavioral biases jointly influence their diversification choices. Younger, lower-income (less wealthy), and relatively less sophisticated investors and those who follow price trends, prefer local (familiar) stocks, and exhibit over-confidence hold relatively less diversified portfolios. Under-diversified investors exhibit strong style and industry preferences and they also prefer more volatile and positively skewed stocks. Furthermore, we find some evidence to support the asymmetric information hypothesis for under diversification. In contrast, we find that factors such as small portfolio size, transaction costs, and search costs are unlikely determinants of investors' diversification choices. The unexpectedly high idiosyncratic risk in investors' portfolios results in a welfare loss.

Suggested Citation

  • William N. Goetzmann & Alok Kumar, 2005. "Why Do Individual Investors Hold Under-Diversified Portfolios?," Yale School of Management Working Papers ysm454, Yale School of Management.
  • Handle: RePEc:ysm:somwrk:ysm454

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    References listed on IDEAS

    1. Jensen, Michael C, 1986. "Agency Costs of Free Cash Flow, Corporate Finance, and Takeovers," American Economic Review, American Economic Association, vol. 76(2), pages 323-329, May.
    2. William N. Goetzmann & Andrey Ukhov & Ning Zhu, 2004. "China and the World Financial Markets 1870-1930:," Yale School of Management Working Papers ysm9, Yale School of Management.
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    Cited by:

    1. Ødegaard, Bernt Arne, 2009. "The diversification cost of large, concentrated equity stakes. How big is it? Is it justified?," Finance Research Letters, Elsevier, vol. 6(2), pages 56-72, June.
    2. Laurent E. Calvet & John Y. Campbell & Paolo Sodini, 2007. "Down or Out: Assessing the Welfare Costs of Household Investment Mistakes," Journal of Political Economy, University of Chicago Press, vol. 115(5), pages 707-747, October.
    3. James Choi & David Laibson & Brigitte Madrian, 2008. "The Flypaper Effect in Individual Investor Asset Allocation," Yale School of Management Working Papers amz2560, Yale School of Management.
    4. Kumar, Alok, 2007. "Do the diversification choices of individual investors influence stock returns?," Journal of Financial Markets, Elsevier, vol. 10(4), pages 362-390, November.
    5. H. Henry Cao & Bing Han & David Hirshleifer & Harold H. Zhang, 2011. "Fear of the Unknown: Familiarity and Economic Decisions," Review of Finance, European Finance Association, vol. 15(1), pages 173-206.
    6. Nicholas Barberis & Ming Huang, 2008. "Stocks as Lotteries: The Implications of Probability Weighting for Security Prices," American Economic Review, American Economic Association, vol. 98(5), pages 2066-2100, December.
    7. Chang, Charles & Fuh, Cheng-Der & Hsu, Ya-Hui, 2008. "ESO compensation: The roles of default risk, employee sentiment, and insider information," Journal of Corporate Finance, Elsevier, vol. 14(5), pages 630-641, December.
    8. Chavas, Jean-Paul & Barham, Bradford, 2007. "On the Microeconomics of Diversification under Uncertainty and Learning," Staff Paper Series 515, University of Wisconsin, Agricultural and Applied Economics.
    9. Jean-Philippe Bouchaud & Damien Challet, 2016. "Why have asset price properties changed so little in 200 years," Papers 1605.00634,
    10. Matus Medo & Chi Ho Yeung & Yi-Cheng Zhang, 2008. "How to quantify the influence of correlations on investment diversification," Papers 0805.3397,, revised Feb 2009.
    11. James J. Choi & David Laibson & Brigitte C. Madrian, 2009. "Mental Accounting in Portfolio Choice: Evidence from a Flypaper Effect," American Economic Review, American Economic Association, vol. 99(5), pages 2085-2095, December.
    12. Ajamu Loving & Michael Finke & John Salter, 2012. "Explaining the 2004 Decrease in Minority Stock Ownership," The Review of Black Political Economy, Springer;National Economic Association, vol. 39(4), pages 403-425, December.
    13. Anderson, Anders, 2005. "Is Online Trading Gambling with Peanuts?," Sonderforschungsbereich 504 Publications 06-02, Sonderforschungsbereich 504, Universität Mannheim;Sonderforschungsbereich 504, University of Mannheim.
    14. Chae, Joon & Yang, Cheol-Won, 2013. "Commonality in individuals' trading: A systematic path between behavioral bias and expected returns," Pacific-Basin Finance Journal, Elsevier, vol. 21(1), pages 1008-1023.

    More about this item

    JEL classification:

    • G11 - Financial Economics - - General Financial Markets - - - Portfolio Choice; Investment Decisions
    • G12 - Financial Economics - - General Financial Markets - - - Asset Pricing; Trading Volume; Bond Interest Rates

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