Investors may be getting a raw deal when investing in index mutual funds through their broker, as they pay a steep "broker penalty." The extra operating costs paid over time for broker-sold load index funds are triple those paid by investors in true no-load mutual funds, according to a study by Zero Alpha Group and Fund Democracy, released during a conference call last week.

The study analyzed 141 retail mutual funds that track the Standard & Poor's 500 index. Data was gathered from Morningstar's Principia Pro Plus for Mutual Funds database.

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