I snipped the graphic below from this article in The Wall Street Journal.
The article makes the point that there seems to be a correlation between account size and profitability .
It’s the smallest and the newest investors that are most likely to lose money. The firms with the highest percentage of profitable accounts, Interactive Brokers and CitiFX, have minimum deposit requirements of $10,000. For some of the others, the minimum is much lower–as little as $50. The average account in the U.S. has about $6,000 to $7,000 on deposit, according to industry research.