Bloomberg

Rigged-Market Theory Scores a Perfect Quarter: Jonathan Weil

May 12, 2010, 9:20 PM EDT

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Commentary by Jonathan Weil

May 13 (Bloomberg) -- Score another triumph for the rigged- market theory.

The intrigue is high. If a too-big-to-fail bank’s traders were able to make money every day of a quarter, were they really trading in any normal sense of the word? Or would vacuuming be a more accurate term? What kinds of risks do such incredible profits entail, for the banks and the rest of us taxpayers? And are results such as these too good to be true?

There seems to be no satisfying way to answer those questions, or even the more basic inquiry: How exactly do these banks’ trading divisions make money? Reading the companies’ impenetrable financial reports is of little help. However they did it, the data suggest it was as easy last quarter as hitting the side of a barn with a baseball from three feet away.

This isn’t the way “trading” works in the real world. A simple exercise in measuring probabilities is instructive here.

Long Odds

Let’s say you manage a highly leveraged, diversified investment fund, and have become so skilled at playing the markets that you have a 70 percent probability of making money any given trading day. This would be a remarkable achievement in most markets. The odds that you would post a daily net gain 63 times in a row, though, would be about one in 5.7 billion. The formula for calculating this is: 1/(0.70 to the 63rd power).

Even if you had a 95 percent likelihood of a winning day, you would have only a 3.9 percent chance of doing it 63 trading sessions in a row. More...