Exchange-traded funds have experienced tremendous growth over the past decade but not all of that growth is positive, according to new research from Vanguard.

As of March 31, more than $1.2 trillion was invested in about 1,400 U.S.-listed ETFs, according to the Valley Forge, P.A.-based fund firm, citing data from Strategic Insight’s Simfund. The report also revealed that U.S.-listed ETFs currently track more than 1,000 different indexes and, increasingly, ETFs have been launched using new indexes based on “narrow market segments and alternative weighting methods that often lack ‘live’ performance history.”

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