Time Variation in the Equity Risk Premium

January 01, 2011

The Research Foundation of CFA Institute

The equity risk premium (ERP) refers to the expected (and sometimes realized) return of a broad equity index in excess of some fixed-income alternative. In the past decade, investors have shifted their thinking about whether to use historical average returns or forward-looking valuation indicators in calculating the ERP.

Academics and practitioners alike used to think the ERP was constant over time, in which case the future premium would best be estimated from the long-run average of the realized excess return. If the historical realized outperformance of stocks over bonds was 6%, for example, 6% would also be the best forecast for the future.

Roller-coaster experiences in markets in the first decade of the 21st century, as well as theoretical and empirical lessons, have converted many observers to the belief that expected returns and premiums vary over time. If so, then past average returns are a highly misleading indicator of future returns. Forward-looking valuation indicators are better and may provide useful timing signals.

Low dividend yields or low earnings yields (or their inverse, high price-to-earnings ratios) are now seen as a sign of low prospective stock-market returns, just as low bond yields and narrow yield spreads are interpreted as forecasting low returns in fixed-income markets. This forward-looking logic would have guided investors well during the low equity market yields of 2000 and high market yields of early 2009.

While this paper focuses on the equity risk premium, investors should remember that relying exclusively or primarily on the ERP as the source of long-run returns causes portfolios to be inadequately diversified.



  • AQR Capital Management, LLC, (“AQR”) provide links to third-party websites only as a convenience, and the inclusion of such links does not imply any endorsement, approval, investigation, verification or monitoring by us of any content or information contained within or accessible from the linked sites. If you choose to visit the linked sites, you do so at your own risk, and you will be subject to such sites' terms of use and privacy policies, over which AQR.com has no control. In no event will AQR be responsible for any information or content within the linked sites or your use of the linked sites.

  • The information contained herein is only as current as of the date indicated, and may be superseded by subsequent market events or for other reasons. The views and opinions expressed herein are those of the author and do not necessarily reflect the views of AQR Capital Management, LLC, its affiliates or its employees.

    This information is not intended to, and does not relate specifically to any investment strategy or product that AQR offers. It is being provided merely to provide a framework to assist in the implementation of an investor’s own analysis and an investor’s own view on the topic discussed herein. Past performance is not a guarantee of future results.