Exchange-traded funds (ETFs) are a fast-growing segment of the mutual-fund business, in large part because they offer investors better control...

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Exchange-traded funds (ETFs) are a fast-growing segment of the mutual-fund business, in large part because they offer investors better control at a low cost.

ETFs are built like an index fund — mimicking the strategy of a benchmark — but trade minute by minute like a stock.

The proliferation of ETFs — including a wide range of new options based on quirky or unusual investment strategies — has left some investors struggling to decide if this is an investment vehicle they want to buy or some gimmick that’s not here for long.

To learn more about ETFs — and to help separate the power tools from the ordinary indexlike funds and the gimmicks — Rydex Investments has created “ETFEssentials,” a page on its Web site that gives a soup-to-nuts explanation of ETFs, including information on pricing, liquidity and more. Go to: rydexinvestments.com.