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When to Put All Your Eggs in One Basket.....When Diversification Increases Portfolio Risk!


  • Cornelis A. Los


Portfolio diversification may not always lower the portfolio risk, but may actually increase it. It depends on the long memory and distributional stability characteristics of the underlying rates of return. This disturbing result is based on the theoretical Fama- Samuelson proposition of 1965-67. However, there exists now ample empirical evidence for such peculiar results, since most financial return series show long memory, e.g., the S&P500 Index return series. Illiquid real estate and bank loan values are sometimes subject to catastrophic discontinuities. Adding these assets to the portfolio may increase its risk drastically.

Suggested Citation

  • Cornelis A. Los, 2004. "When to Put All Your Eggs in One Basket.....When Diversification Increases Portfolio Risk!," Finance 0411037, EconWPA.
  • Handle: RePEc:wpa:wuwpfi:0411037
    Note: Type of Document - pdf; pages: 7

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    References listed on IDEAS

    1. Harry Markowitz, 1952. "Portfolio Selection," Journal of Finance, American Finance Association, vol. 7(1), pages 77-91, March.
    2. Samuelson, Paul A., 1967. "Efficient Portfolio Selection for Pareto-Lévy Investments," Journal of Financial and Quantitative Analysis, Cambridge University Press, vol. 2(02), pages 107-122, June.
    3. Eugene F. Fama, 1965. "Portfolio Analysis in a Stable Paretian Market," Management Science, INFORMS, vol. 11(3), pages 404-419, January.
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    Cited by:

    1. Cornelis A Los, 2005. "Why VaR FailsLong Memory and Extreme Events in Financial Markets," The IUP Journal of Financial Economics, IUP Publications, vol. 0(3), pages 19-36, September.
    2. Camilleri, Silvio John & Galea, Gabriella, 2009. "The Diversification Potential Offered by Emerging Markets in Recent Years," MPRA Paper 62491, University Library of Munich, Germany.

    More about this item


    portfolio management; distibutional stability; long memory; financial risk;

    JEL classification:

    • G12 - Financial Economics - - General Financial Markets - - - Asset Pricing; Trading Volume; Bond Interest Rates
    • G13 - Financial Economics - - General Financial Markets - - - Contingent Pricing; Futures Pricing
    • G14 - Financial Economics - - General Financial Markets - - - Information and Market Efficiency; Event Studies; Insider Trading
    • C23 - Mathematical and Quantitative Methods - - Single Equation Models; Single Variables - - - Models with Panel Data; Spatio-temporal Models

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