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By Ian Ayres, August 31 2007, FT.com

Six years ago, Ted Ruger, a law professor at the University of Pennsylvania, attended a seminar at which two political scientists, Andrew Martin and Kevin Quinn, made a bold claim. They said that by using just a few variables concerning the politics of the case, they could predict how the US Supreme Court justices would vote.

Analysing historical data from 628 cases previously decided by the nine Supreme Court justices at the time, and taking into account six factors, including the circuit court of origin and the ideological direction of that lower court's ruling, Martin and Quinn developed simple flowcharts that best predicted the votes of the individual justices. For example, they predicted that if a lower court decision was considered "liberal", Justice Sandra Day O'Connor would vote to reverse it. If the decision was deemed "conservative", on the other hand, and came from the 2nd, 3rd or Washington DC circuit courts or the Federal circuit, she would vote to affirm.

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