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Do We Really Know That Financial Markets Are Efficient?

Listed author(s):
  • Lawrence H. Summers

This paper examines the power of statistical tests commonly used to examine the efficiency of speculative markets. It shows that for markets with "long horizons" such as the stock markets, or the market for long term bonds, these tests have very low power. Market valuations can differ substantially and persistently from the rational expectation of the present value of cash flows without leaving statistically discernible traces in the pattern of ex-post returns. This observation also suggests that speculation is unlikely to insure rational valuations, since similar problems of identification plague both financial economists and would-be speculators.

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File URL: http://www.nber.org/papers/w0994.pdf
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Paper provided by National Bureau of Economic Research, Inc in its series NBER Working Papers with number 0994.

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Date of creation: Sep 1982
Publication status: published as Summers, Lawrence H. "Do We Really Know that Financial Markets are Efficient?" Corporate Financial Policy, ed. J. Edwards. New Yotk, Cambridge University Press, 1986, pp. 13-24
Handle: RePEc:nbr:nberwo:0994
Note: EFG PE
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  1. Shiller, Robert J, 1979. "The Volatility of Long-Term Interest Rates and Expectations Models of the Term Structure," Journal of Political Economy, University of Chicago Press, vol. 87(6), pages 1190-1219, December.
  2. David S. Jones & V. Vance Roley, 1982. "Rational Expectations, the Expectations Hypothesis, and Treasury Bill Yields: An Econometric Analysis," NBER Working Papers 0869, National Bureau of Economic Research, Inc.
  3. Olivier J. Blanchard & Mark W. Watson, 1982. "Bubbles, Rational Expectations and Financial Markets," NBER Working Papers 0945, National Bureau of Economic Research, Inc.
  4. Shiller, Robert J, 1981. "Do Stock Prices Move Too Much to be Justified by Subsequent Changes in Dividends?," American Economic Review, American Economic Association, vol. 71(3), pages 421-436, June.
  5. Friedman, Benjamin M., 1979. "Optimal expectations and the extreme information assumptions of `rational expectations' macromodels," Journal of Monetary Economics, Elsevier, vol. 5(1), pages 23-41, January.
  6. Ibbotson, Roger G & Sinquefield, Rex A, 1976. "Stocks, Bonds, Bills, and Inflation: Year-by-Year Historical Returns (1926-1974)," The Journal of Business, University of Chicago Press, vol. 49(1), pages 11-47, January.
  7. Richard Meese & Kenneth S. Rogoff, 1981. "Empirical exchange rate models of the seventies: are any fit to survive?," International Finance Discussion Papers 184, Board of Governors of the Federal Reserve System (U.S.).
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