As specialized exchange-traded-funds expand into additional market sectors and niches, some observers believe investors are becoming confused and the overabundance is pushing ETFs further from their roots as low-cost, tax-efficient investments, The Wall Street Journal reports.

Typically, ETFs track benchmarks such as Standard & Poor's 500-stock index or the Dow Jones Industrial Average, but they are increasingly expanding into domestic exchanges and concentrating on focused portfolios.

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