According to a recent article in Entrepreneur magazine, micro-cap stocks (stocks with a market cap between $50 million and $500 million) increased 72.3 percent over the past five years.

In the past, if you wanted to track micro-cap stock performance, you had to buy micro-caps individually or buy an index fund that tracked the Russell 2000 (small-cap index). Now, however, there's a new Russell index…in addition to the Russell 3000, 2000, and 1000 indexes, there's The Russell Micro-cap Index.

According to Russell.com, the "Russell Microcap Index measures performance of the microcap segment, representing less than 3% of the U.S. equity market. The Russell Microcap Index includes the smallest 1,000 securities in the small-cap Russell 2000 Index plus the next 1,000 securities."

New ETF's are cropping up to reflect the new micro-cap index.

According to Entrepreneur magazine…

Until recently, interested investors had to settle for purchasing individual micro-caps or a handful of mutual funds that play in the micro-cap arena. These are risky and high-priced options, respectively. But no more: The past six months have seen the launch of three exchange-traded funds, or ETFs, that make buying a basket of microcaps both cheap and accessible. WIth expense ratios of 0.6 percent (vs. 1.58 percent and up for mutual funds), the iShares Russell Microcap Index fund, the PowerShares Zacks Micro Cap Portfolio, and the First Trust Microcap ETF each track a microcap index and employ stock screening to create a pool of 250 to 450 micro-caps."