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interest rate ris

Expert Analysis and Commentary

Interest Rate Risk and the Low-Volatility Anomaly

Larry Swedroe Sep 14, 2016



The superior performance of low-volatility stocks was first documented in the literature in the 1970s, by Fischer Black (in 1972) among others, before the size and value premiums were “discovered.” The low-volatility anomaly has been shown to exist in equity markets around the globe. Interestingly, this finding holds true not only for stocks, but for bonds as well. In other words, it has been pervasive.

One of CAPM’s assumptions is that there are no constraints on either leverage or short selling. In the real world, many investors are, in fact, constrained against the use of leverage (through their charters) or have an aversion to its use. The same is true of short selling. Plus, the borrowing costs for certain difficult-to-borrow stocks may be quite high. Such limits can prevent arbitrageurs from correcting the pricing mistake. Another assumption made by CAPM is that markets have no frictions, meaning there are neither transaction costs nor taxes. Of course, in the real world, there are costs. The evidence shows that the most mispriced stocks are those with the highest costs of shorting.

The explanation for the low-volatility anomaly is that when faced with constraints and frictions, investors looking to increase their returns choose to tilt their portfolios toward high-beta securities to garner more of the equity risk premium. This extra demand for high-beta securities, and reduced demand for low-beta securities, may explain the flat or even inverted relationship between risk and expected return relative to the predictions of CAPM.

More recent research on the low-volatility anomaly has found that once profitability is included as a factor, low-volatility performance is well explained by controlling for the common investment factors of size, value and profitability. In addition, research has also found that low-volatility strategies have exposure to term risk (the duration factor). This should not be a surprise because, generally speaking, low-volatility (or low-beta) stocks are more “bond like.” They are typically large stocks, the stocks of profitable and dividend-paying firms, and the stocks of firms with mediocre growth opportunities. In other words, they are stocks with the characteristics of safety, as opposed to risk and opportunity. Thus, they show higher correlations with long-term bond returns.


  • The duration of the lowest-volatility decile corresponds to a 30 percent weight to bonds.
  • The duration of the highest-volatility decile corresponds to a position of 100 percent short bonds.
  • Term risk helps explain the low-volatility anomaly.
  • Depending on the methods chosen, term exposure explains between 19 percent and 99 percent of the monthly return difference between the lowest-volatility and the highest-volatility deciles.
  • Interestingly, they found that exposure of low-volatility stocks to term risk varied over time. In the 1970s, low-volatility stocks were no different in their exposure to term risk than high-volatility stocks. However, beginning in the mid-1980s, the exposure to term risk began to increase and has since remained high.
  • Their basic conclusions were not altered when different bond maturities were used for the term factor.


The Bottom Line


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