Related: A Defensive Sector ETF for Volatile Summer Months

Supporting the low-vol performance, MSCI pointed to beta, the degree to which stocks tend to move in the same direction as the market, along with dividend yields. Low-vol ETFs have been strengthening this year as they limited downside risk when the markets slipped and strengthened on increased defensive bets during turbulent times.

About half of XMLV’s lineup “is invested in insurance companies, real estate investment trusts and other financials. Utility (a sector known for steady performance), industrial, materials, high-tech, consumer and health care stocks make up smaller portions of the portfolio,” according to IBD.

Other smart beta mid-cap ETFs include the First Trust Mid Cap Core AlphaDEX Fund (NYSEArca: FNX). The fund selects stocks from the S&P 400 Index, but chooses stocks based on growth factors, sales to price and one year sales growth, along with value factors like book value to price, cash flow to price and return on assets.

For more information on the low-vol strategy, visit our low-volatility category.

PowerShares S&P MidCap Low Volatility Portfolio