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Mean reversion in stock prices : Evidence and Implications


  • Poterba, James M.
  • Summers, Lawrence H.


This paper analyzes the statistical evidence bearing on whether transitory components account for a large fraction of the variance in common stock returns. The first part treats methodological issues involved in testing for transitory return components. It demonstrates that variance ratios are among the most powerful tests for detecting mean reversion in stock prices, but that they have little power against the principal interesting alternatives to the random walk hypothesis. The second part applies variance ratio tests to market returns for the United States over the 1871-1986 period and for seventeen other countries over the 1957-1985 period, as well as to returns on individual firms over the 1926- 1985 period. We find consistent evidence that stock returns are positively serially correlated over short horizons, and negatively autocorrelated over long horizons. The point estimates suggest that the transitory components in stock prices have a standard deviation of between 15 and 25 percent and account for more than half of the variance in monthly returns. The last part of the paper discusses two possible explanations for mean reversion: time varying required returns, and slowly-decaying "price fads" that cause stock prices to deviate from fundamental values for periods of several years. We conclude that explaining observed transitory components in stock prices on the basis of movements in required returns due to risk factors is likely to be difficult.
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Suggested Citation

  • Poterba, James M. & Summers, Lawrence H., 1988. "Mean reversion in stock prices : Evidence and Implications," Journal of Financial Economics, Elsevier, vol. 22(1), pages 27-59, October.
  • Handle: RePEc:eee:jfinec:v:22:y:1988:i:1:p:27-59

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    References listed on IDEAS

    1. Stewart C. Myers & Nicholas S. Majluf, 1984. "Corporate Financing and Investment Decisions When Firms Have InformationThat Investors Do Not Have," NBER Working Papers 1396, National Bureau of Economic Research, Inc.
    2. Myers, Stewart C. & Majluf, Nicholas S., 1984. "Corporate financing and investment decisions when firms have information that investors do not have," Journal of Financial Economics, Elsevier, vol. 13(2), pages 187-221, June.
    3. Smith, Clifford Jr., 1986. "Investment banking and the capital acquisition process," Journal of Financial Economics, Elsevier, vol. 15(1-2), pages 3-29.
    4. Barclay, Michael J. & Smith, Clifford Jr., 1988. "Corporate payout policy : Cash Dividends versus Open-Market Repurchases," Journal of Financial Economics, Elsevier, vol. 22(1), pages 61-82, October.
    5. Keim, Donald B., 1983. "Size-related anomalies and stock return seasonality : Further empirical evidence," Journal of Financial Economics, Elsevier, vol. 12(1), pages 13-32, June.
    6. Myers, Stewart C. & Majluf, Nicolás S., 1945-, 1984. "Corporate financing and investment decisions when firms have information that investors do not have," Working papers 1523-84., Massachusetts Institute of Technology (MIT), Sloan School of Management.
    7. Smith, Clifford Jr., 1977. "Alternative methods for raising capital : Rights versus underwritten offerings," Journal of Financial Economics, Elsevier, vol. 5(3), pages 273-307, December.
    8. Gibbons, Michael R & Hess, Patrick, 1981. "Day of the Week Effects and Asset Returns," The Journal of Business, University of Chicago Press, vol. 54(4), pages 579-596, October.
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