“The S&P 500 Low Volatility Index,” the study said, “tends to rise less than when the market is up, and tends to decline less than the market when the market is down—and that’s why overall volatility is lower than that of the S&P 500.”

S&P Dow Jones Indices officials say their reductions in volatility have been found across various equity categories from a quarter century of data. They say the greatest index volatility reductions have been seen in emerging markets. The strategy, they add, can be an effective tool for many financial advisors.

“I had advisors coming to me a few years ago saying that they were looking for a money preservation strategy,” says Craig Lazzara, managing director, Index Investment Strategy at S&P Dow Jones Indices. He says that adopting this strategy is appropriate for advisors with considerable assets. The advisor, he adds, can bring clients through bad times with below-average losses and still be in a position to reap most of the gains from bull markets.

Then there is the low vol anomaly. From 1968 to 2013, Morningstar’s Alex Bryan notes in a recent report, “the least volatile fifth of the U.S. market actually offered higher returns than the most volatile fifth.”

The debate over why this is, Lazzara adds, has been going on for over 40 years. The anomaly effect was noticed in 1972 by Fischer Black, Michael Jensen and Myron Scholes. Other researchers have since found supporting evidence.

Still, critics contend investors seeking less risk should just buy a few more bonds or perhaps some balanced stocks. And, in a recent paper, two Low Vol dissenters warned that history is not clearly on the side of this supposed low-risk approach.

“What seems to attract investors … is that this lower volatility did not come at the cost of lower returns, at least from 1970 to 2013. However, from 1929 to 1969, returns and volatility were positively related,” according to Bhanu Singh and Marlena Lee, researchers with Dimensional Fund Advisors. In other words, you still need to endure that volatility for better performance.

In their recent paper, “Smart Beta,” the DFA analysts criticize the Low Vol strategy as lacking consistency—that it is, in fact, an inconsistent form of value investing. “The historical record shows that low volatility strategies sometimes emphasize value and sometimes do not,” they write.

“This style drift should not be surprising, given that the low volatility strategy was not designed with valuation in mind.” Singh and Lee warn that investors shouldn’t expect the Low Vol anomaly to be “continuously positioned to capture these premiums.”

But Low Vol advocates contend that theirs is a low cost/low risk approach. With value investments, one buys on the cheap so, when stocks head south, the investor isn’t hurt as much.

What are these low cost buys?

Stocks in the index tend to be consumer staples. They are companies offering products that people usually buy even when the country is in recession or when markets are reeling or both. So while these companies also go through hard times along with the rest of the market, they don’t shed as much blood. Altria Group, Walmart, Colgate-Palmolive, McDonald’s Corp. and Procter & Gamble are among such companies.