Are Stocks Really Less Volatile in the Long Run?

54 Pages Posted: 26 Feb 2009

See all articles by Lubos Pastor

Lubos Pastor

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)

Multiple version iconThere are 3 versions of this paper

Date Written: February 2009

Abstract

According to conventional wisdom, annualized volatility of stock returns is lower when computed over long horizons than over short horizons, due to mean reversion induced by return predictability. In contrast, we find that 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. Mean reversion contributes strongly to reducing long-horizon variance, but it is more than offset by various uncertainties faced by the investor, especially uncertainty about the expected return. The same uncertainties also make target-date funds undesirable to a class of investors who would otherwise find them appealing.

Suggested Citation

Pastor, Lubos and Stambaugh, Robert F., Are Stocks Really Less Volatile in the Long Run? (February 2009). NBER Working Paper No. w14757. Available at SSRN: https://ssrn.com/abstract=1349590

Lubos Pastor (Contact Author)

University of Chicago - Booth School of Business ( email )

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Centre for Economic Policy Research (CEPR)

London
United Kingdom

National Bureau of Economic Research (NBER)

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Robert F. Stambaugh

University of Pennsylvania - The Wharton School ( email )

The Wharton School, Finance Department
University of Pennsylvania
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United States
215-898-5734 (Phone)
215-898-6200 (Fax)

National Bureau of Economic Research (NBER)

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Cambridge, MA 02138
United States

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