The iShares Russell 2000 ETF (NYSEArca: IWM) has only increased 2.1% year-to-date, whereas the SPDR S&P 500 ETF (NYSEArca: SPY) has gained 11.6%.

Moreover, active managers’ overweight tech and energy positions also pressured their portfolios after global growth concerns, high stock valuations and declining oil prices weighed on the sectors.

Due to the persistent underperformance in the active space, more investors are turning to index funds and ETFs. According to ETFGI data, U.S. listed ETFs attracted $199 billion in assets over the first three quarters of 2014, bringing the total ETF assets under management to $2.6 trillion worldwide.

For more information on index-based ETFs, visit our indexing category.

Max Chen contributed to this article.