Portfolio strategist Lily Calcagnini said in a note to clients that the firm's models show the Russell 2000 small-cap index should outperform over the next 12 months. "The Russell 2000 should rise by 14% during the next 12 months, according to a simple model based on US economic growth and starting valuations that has explained roughly two-thirds of Russell 2000 returns between 1995 and 2015," the note said. There are many ETFs that offer investors exposure to the small-cap space, including several large index funds with low fees. The iShares Core S & P Small-Cap ETF (IJR) is the largest small-cap ETF with more than $67 billion and an expense ratio of 0.06%. While the broad index funds above have all returned less than 10% this year, some active funds have seen better results.

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Persons: Goldman Sachs, Lily Calcagnini, Russell, Goldman, Dow Jones, Janus Henderson, — CNBC's Michael Bloom Organizations: BlackRock, Vanguard, Schwab U.S, Dow, Growth Alpha, Pacer