Exchange-traded funds set a record $351 billion in global flows for 2015, according to a recent PwC report.

The PwC report titled “ETFs: A roadmap to growth” finds that survey participants expect even more ETF growth across North America, Europe and Asia, with global ETF assets expected to exceed $7 trillion by 2021.

The North American ETF market is the primary driver of global growth, accounting for more than two-thirds of global ETF assets, according to PwC.

To determine what key developments will help drive further ETF growth, PwC surveyed executives from approximately 60 firms around the world in 2015, of which 18 were from North America. More than 70% of the participants were ETF managers or sponsors, with the remaining participants divided between asset managers not currently offering ETFs and service providers.

Looking at PwC’s findings for just the North American sector, here are three trends that will have an impact on the ETF industry in the near future:

1. The regulatory environment continues to play a key role in shaping the ETF market.

Recent regulatory changes that impact the ETF industry include Securities and Exchange Commission reforms that addressed the use of derivatives and leverage by ETFs and increased disclosure of liquidity risk management efforts by open-ended funds.

In September 2015, the SEC proposed a series of liquidity rules that could significantly affect ETFs, including requiring them to have a liquidity risk management program.

Meanwhile, the SEC’s proposed derivative rules could impact both existing and proposed ETFs, including limiting the use of derivatives by some leveraged and inverse leveraged exchange-traded products.

Most recently, the Department of Labor’s fiduciary standard rule, released in April, requires any advice provided to an employee benefit plan or an individual retirement account must be in the best interests of the investor.

“The fiduciary standard rule has the potential to further align the interests of financial advisors and investors by shifting away from investments in commission-based products and moving them towards lower cost, fee-based investment products such as ETFs,” PwC states.

2. The approval of nontransparent ETFs is the most important development over the next five years.

Virtually all North American participants in the PwC survey agree that periodically disclosed ETFs — so-called nontransparent ETFs like Eaton Vance’s NextShares — will change the ETF landscape in a way that would have an effect on their firm’s operations, according to the report.

“The biggest impact, according to those in our survey, will be the downward pressure they exert on fees charged by actively managed mutual funds,” PwC states.

According to the survey, 57% of North American respondents expect periodically disclosed active ETFs to put pressure on active mutual fund fees, and 43% expect the funds to impact overall ETF growth. “They are also likely to contribute to asset growth, not least of all by introducing more investors to the world of ETFs,” PwC states.

However, PwC expects that active ETF sponsors will have to have some type of revenue sharing program to provide an incentive to encourage sales of active ETFs.

3. Another important development is the approval of generic listing requirements for active ETFs.

According to PwC, the U.S. active ETF market has been slowly growing since their introduction in 2007. Most of this growth is coming from active fixed income ETFs that have less risk to potential front-running of the portfolio, according to PwC.

“This slow growth is a direct result of the SEC requirement to provide daily transparency,” the report states. “More than 75 firms have obtained approval from the SEC to launch transparent active ETFs, while there are only 30 active ETF issuers as of Feb. 5, 2016.”

Half of all North American survey participants expect assets in active ETFs to grow from less than $20 billion to more than $100 billion in three years or less, while the other half expect it to take more than three years.

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