Forty-one per cent of surveyed investors said that they were very concerned, while 49 per cent were somewhat concerned.

A majority of investors see the risks of swap-based ETFs as the main reason for not investing in the product, according to the survey.

At the same time, nearly half of investors said that ETF investments make up between 5 and 19 per cent of their portfolios.

For the survey, Morningstar surveyed 593 investors, 92 of them professional.

The costs and structure of the ETF market have come under scrutiny recently and some figures in the industry are concerned that some of them are opaque and over-complex, especially swap-based products.

Last month, two of the industry’s giants announced steps to shake up the market and address the concerns of investors and regulators. iShares, the world’s largest ETF platform, part of BlackRock, launched a European initiative called due diligence, aimed at helping investors to evaluate exchange-traded products. Elsewhere, Lyxor, another big hitter in the ETF market and part of Société Générale, launched a quality charter for its clients, which aims to make these vehicles more transparent.

In the third quarter of 2011 the ETF market held around $1.4 trillion of assets, up from $1.3 trillion in the third quarter of last year, according to iShares.