Small-cap and mid-cap stocks have been able to find relative refuge amid the market turbulence, and there are a number of ETF choices that can take advantage of this trend.ETFs that track these two areas have been outperforming the market in the first half of the year. The iShares S&P Small Cap 600 Index ( IJR) is trading right around where it was at the beginning of the year, while the iShares S&P Mid Cap 400 Index ( IJH) is up 2.5% year to date. Overall, these might not be eye-catching performances, but they compare quite favorably to the S&P 500, which is down 7.3% so far this year. The returns that these ETFs have afforded investors underscore the value that can be achieved with even a slight degree of fine-tuning to an index investor's portfolio. "There is plenty of benefit in being somewhat active in picking niche sub-index ETFs," says Will McClatchy, Founder and Editor of ETFZone.com. "If you want to be active, pick sub-index ETFs." Sub-index ETFs have been gaining an increasing amount of attention as the broader markets have continued to remain volatile. Within the small-cap and mid-cap space, there are ETFs geared toward growth investors as well as value investors. The Vanguard Small Cap Growth ETF ( VBK) has been ahead of the market thus far in 2008 with a -0.5% return. Its holdings include names such as Priceline.com ( PCLN), Petrohawk Energy ( HK) and FLIR Systems ( FLIR). Another sub-index ETF that has performed particularly well relative to the S&P 500 is the iShares S&P Mid Cap 400 Growth Index ( IJK). It is up 3.7% year to date and holds positions in companies such as Southwestern Energy ( SWN), Intuitive Surgical ( ISRG) and Cleveland-Cliffs ( CLF).