Hieronymous analysed 462 speculative trading accounts of a major brokerage firm over the period of a year in 1969. The accounts traded the full range of commodity contracts available at that time. In the course of the year, 164 accounts showed profits and 298 accounts showed losses, that is to say that just over a third of traders made money.
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The lesson? A lot of people enter unprepared, take a loss and then quickly leave with burnt fingers. Those that stick around to play the game can be winners, but not the majority.

Ronald L. Johnson prepared a report for the North American Securities Administrators Association (NASAA, a consumer protection group trying to keep the futures industry honest) on the success of retail traders.He chose at random 30 accounts (not a very big sample size, I'll agree) from a retail trading firm.
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This study found that 18 of the 26 accounts lost money. In addition, risk of ruin calculations on the trader's statistics found that in theory, three quarters of the sample were headed inexorably toward failure, with a 100% risk of ruin.
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Conclusions of this study: the great majority of traders surveyed had a risk of ruin so high as to make eventual bankruptcy virtually inevitable. The traders with the shortest time frames (day traders) lost the most money and had the highest risk of ruin.