Responding to the increasing popularity of exchange-traded funds, the assets of which have grown 36% over the past year to $9.32 trillion, asset management firms continue to bring new ETF products to market, The Wall Street Journal reports.

But since all of the traditional indexes are already being tracked by ETFs, new offerings either adjust these indexes or track small sectors of the market. Instead of modifying an index to invest more heavily in companies with larger market capitalizations, for instance, some of the new ETFs look for companies with the largest dividends, revenue or cash flow. And many of the new offerings track small sectors, such as drug companies or consumer goods.

"The ETF industry is moving beyond traditional indexes that are market-cap-weighted to more creative formulas," said Ronald DeLegge, publisher of "If ETFs are only based on benchmark indexes, there is only the need for so many," added Bruce Bond, president of PowerShares, which offers 35 ETFs.

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