The value factor trailed its growth and momentum rivals last year, but some investors are betting value stocks will rebound in 2018. That could spark renewed attention on value exchange traded funds, including the Guggenheim S&P 500 Pure Value ETF (NYSEArca: RPV).

The value play may be seen as a basic type of enhanced or smart beta ETF strategy that specifically targets value stocks that tend to trade at a lower price relative to fundamentals, like dividends, earnings and sales. Along with the simple pure value play, such as RPV, the other value-focused ETFs may also incorporate other factors in their screening process.

RPV gained 17.3% in 2017, trailing the S&P 500 by 440 basis points. Value stocks usually trade at lower prices relative to fundamental measures of value, like earnings and the book value of assets. On the other hand, growth-oriented stocks tend to run at higher valuations since investors expect the rapid growth in those company measures, but more are growing wary of high valuations.

“Other value ETFs have been picking up bargains, while the rest of the universe obsesses over growth. Another standout is Guggenheim Investments’ S&P Pure Value ETF,” reports Reuters. “It sifts through the S&P 500, eliminates all growth stocks and the so-called ‘muddle in the middle,’ and comes up with 114 pure value plays.”

Value stocks typically cover companies that trade at a lower price relative to fundamentals such as dividends earnings and sales, which are then considered undervalued by a value investor.

“The $890-million fund also boasts an affordable expense ratio of .35 percent. In the fund’s rebalancing in December financial and utilities were trimmed back, thanks to their recent runups, while consumer discretionary stocks were boosted,” according to Reuters. “A word of caution for value-minded investors: Such deep-value and pure-value screens tend to make holdings more limited, and therefore more volatile, than broader market indices.”

Value stocks have historically outperformed growth stocks, or companies with high earnings expectations, in almost every market over the long-haul. For instance, the MSCI USA Value Index has outperformed the MSCI USA Growth Index by an annualized 81 basis points since 1974 through September 2015.

RPV allocates over 28% of its weight to financial services stocks and over 20% to the consumer discretionary sector. Energy and healthcare names combine for about 22%.

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