Exchange-traded funds, long hailed as a godsend by offering cheap and easy access to basically any sector, asset class, region, or strategy on the market, may be giving rise to a bad habit that experts say can erode investors’ returns.

Such critics warn that ETFs are being overtraded, with investors increasingly jumping in and out of an asset rather than buying and holding it for potential long-term gains.

The intraday tradability of ETFs, which typically hold a basket of securities but trade like stocks, has made them a favorite tool for short-term positioning and portfolio hedges, and so widely have they been adopted that of the market’s 15 most active securities, 14 are ETFs. By contrast, mutual funds only price and trade at the end of a trading session, making them ill-suited for reacting to breaking news, for example.

Read more:Here’s how much ETFs are dominating on the trading floor

The ease of trading ETFs, however, is where the risk comes in. Each market move, whether a buy or sell, comes with various costs that reduce the returns of even successful bets. And it is notoriously difficult—basically impossible—to time the market over long periods. That means day traders and speculators face high hurdles to profitability. Furthermore, making short-term bets means that investors miss out on the benefits of compound interest, which can amplify investment returns over long-term time horizons.

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No less an authority than Jack Bogle—the former chief executive of Vanguard, considered the father of passive investing—has criticized ETFs for how they can lead to overuse. In a December op-ed in the Financial Times, Bogle reflected on how he turned down the opportunity to create the first ETF, which became the SPDR S&P 500 ETF Trust SPY, -1.15% , citing the intraday trading issue.

“I could not agree with such a trading mentality,” he wrote. “Time and again, clear statistical evidence has confirmed that the more investors trade, the more their returns fall short of the stock market return.”

Read:Here’s why you shouldn’t buy a stock ever again

The amount a return can fall short obviously depends on the fund and how long the investor holds it, but the difference can be dramatic. According to Terrance Odean, a professor at the University of California, Berkeley who recently gave a presentation on investor behavior to the Securities and Exchange Commission, the most active traders can see about half the return of their buy-and-hold peers.

A slide from Odean’s recent presentation, which was based on research he did with Brad Barber, a professor at the University of California, Davis.

This issue is pronounced along gender lines, according to a 2001 paper Odean wrote that analyzed trading records for more than 35,000 households. “Psychological research demonstrates that, in areas such as finance, men are more overconfident than women. We document that men trade 45% more than women. Trading reduces men’s net returns by 2.65 percentage points a year as opposed to 1.72 percentage points for women.”

Perhaps not surprisingly, this form of overconfidence is most acute among single men, who may have less experience or a greater risk tolerance than their married peers.

“Single men trade 67% more than single women thereby reducing their returns by 1.44 percentage points a year more than do single women,” the report read.

The average annual portfolio turnover for single men is around 90%, according to Odean, compared with about 80% for men overall. Women have annual turnover below 60%, while single women do the least trading of all, with a turnover of about 50%.

Obviously, many ETF investors can and do hold funds for years, getting all the benefits of index-based investing, as well as the additional benefits that come from the ETF structure. Compared with mutual funds, ETFs charge lower fees on average and have greater tax efficiency, making them a more cost-effective instrument for long-term holdings.

The trick, of course, is that they have to actually be held for the long term.