(Dow Jones) Early signs suggest ETFs played a big role in Thursday's turmoil. It's too early to tell if they were victims or somehow contributors to the problem.

About one-fifth of the exchange-traded funds were at least temporarily snarled in trading glitches that took place Thursday, according to Morningstar Inc. (MORN) trading data. Meanwhile, a separate report by ETF site indexuniverse.com analyzing lists of canceled trades by Nasdaq and the New York Stock Exchange suggests more than half the securities on those lists were ETFs rather than individual stocks.

It isn't immediately clear why ETFs, baskets of stocks that trade throughout the day, would be disproportionately affected by trading problems. ETFs are, however, famously popular with active traders and, sometimes representing the prices of hundreds of individual stocks, add a level of complexity to trading moves.

About 210 out of 980 exchange-traded funds changed hands at some point Thursday at a price more than 50% below their ultimate closing price, according to fund research Morningstar, which like many stock quotation systems records daily highs, lows and closing prices.

Among the strange results: the $11 billion iShares Russell 1000 Growth ETF (IWF), which changed hands at one point for a penny; the $2.7 billion Vanguard Mid Cap ETF (VO) and the $5.3 billion iShares S&P 500 Growth Index (IVW), which both traded for 10 cents.

It wasn't immediately clear how many shares of these popular funds actually traded at such aberrant-looking prices or how long the strange behavior lasted. Each of those funds recovered to record a closing price at a level that was within a dollar or two of its high.

Indexuniverse, which analyzed a list of canceled trades on 281 securities published by Nasdaq, found about two-thirds were ETFs. On a similar list of 173 securities put out by the New York Stock Exchange about three in five were ETFs, the site said.

BlackRock Inc. (BLK) and Vanguard didn't immediately provide comments on the trading. The NYSE and Nasdaq didn't immediately return calls for comment.


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