The risks cut both ways: Too much stock can bring slower turnover and cash flow, while too little can mean lost sales.

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The average stock fund has a turnover in the vicinity of 100% , which means that in the space of 12 months it buys and sells an amount of stock equal to its net assets.

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Last year, turnover at the New York Stock Exchange, the world's busiest, reached six times the level of 1982.

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Among its plethora of distractions are depressed earnings and stock price, high-level executive turnover and a possible takeover attempt led by company founder Richard Schulze.

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Because the ETF trades like any other stock, the investor should also examine the daily turnover of the ETF itself for much the same reason.

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From 1993 to 1997, the value of their stock purchases averaged 0.77% of the total market turnover.

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For Passport this is an important number because Stouffer trades as if stock exchanges were going out of style. (Portfolio turnover: 700% a year.) You're not going to have any luck getting this stat from the folks manning the toll-free number.

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Perhaps you should go all the way to a cheap index fund, like Vanguard Index Total Stock Market, which has both low expenses (0.2% annually) and rock-bottom turnover (3% ).

FORBES: The hidden cost of trading

Over the six years that Marketocracy has monitored his portfolio, Rees has had turnover in excess of 200% in the last 12 months, and his winning percentage on stock picks is a whopping 88%.

FORBES: Magazine Article