Are Stocks Really Less Volatile in the Long Run?
University of Chicago - Booth School of Business; Centre for Economic Policy Research (CEPR); National Bureau of Economic Research (NBER)
Robert F. Stambaugh
University of Pennsylvania - The Wharton School; National Bureau of Economic Research (NBER)
CEPR Discussion Paper No. DP7199
Conventional wisdom views stocks as less volatile over long horizons than over short horizons due to mean reversion induced by return predictability. In contrast, we find stocks are substantially more volatile over long horizons from an investor's perspective. This perspective recognizes that parameters are uncertain, even with two centuries of data, and that observable predictors imperfectly deliver the conditional expected return. We decompose return variance into five components, which include mean reversion and various uncertainties faced by the investor. Although mean reversion makes a strong negative contribution to long-horizon variance, it is more than offset by the other components. Using a predictive system, we estimate annualized 30-year variance to be nearly 1.5 times the 1-year variance.
Number of Pages in PDF File: 48
Keywords: long-run, risk, stock, variance
JEL Classification: G11, G23working papers series
Date posted: March 11, 2009
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