Looking ahead, Cogent found that advisors are expected to raise their ETF allocations even further in the coming months, mainly at the expense of mutual funds, as more become acquainted with the relatively cheap and efficient ETF investment vehicle. [Why Consider the ETF Investment Vehicle]

Advisors have also exhibited growing interest in rules-based, smart-beta ETFs. For instance, the most popular ETFs of the year include those that track a currency-hedged strategy, including the WisdomTree Europe Hedged Equity Fund (NYSEArca: HEDJ) and Deutsche X-trackers MSCI EAFE Hedged Equity ETF (NYSEArca: DBEF), which have seen $15.6 billion and $12.8 billion in net inflows year-to-date. [Investors are Ditching U.S. Stocks in Favor of International ETFs]

The smart-beta segment is one of the fastest growing areas of the ETF industry. There are now 478 enhanced U.S.-listed ETF strategies, with $245.6 billion in assets under management, according to XTF data. These enhanced ETFs track alternative indices that do not follow traditional market capitalization methodologies.

For more information on the ETF industry, visit our current affairs category.

Max Chen contributed to this article.