U.S. Supreme Court Votes Can Be Predicted: Study

Judicial philosophies or past decisions can be clues into how U.S. Supreme Court justices will decide a case, but a study published Wednesday suggests that looking at the justices' voting patterns may be just as good an indicator.

The authors of the report, researchers Roger Guimera and Marta Sales-Pardo of Spain, set out to ask whether one of the nine Supreme Court justices could be plucked from the bench and replaced with an algorithm that does not take into account the law or the case at issue, but does take into account the other justices' votes and the court's record.

Predicting a Justice's Decision Bases on Other Justices' Votes

These researchers say their computational models, using methods developed to analyze complex social networks, are just as accurate in predicting a justice's decision as forecasts from legal experts.

We find that Supreme Court justices are significantly more predictable than one would expect from 'ideally independent' justices in 'ideal courts,' that is, free agents independently evaluating cases on their merits, free of ideology, the study said.

The study was based on 150 cases of each court beginning with the Warren court in 1953 and ending with the Rehnquist court in 2004.

'Block Method' More Predictive Than Ideology

In using a block method, grouping justices and cases, the researchers' model correctly predicted 83 percent of votes, compared with 67.9 percent from legal experts in one study and 66.7 percent from a case-content-based algorithm.

The study also said that predictability of justices changes over time and fluctuates depending on the party occupying the White House. The study said that court predictability is lower during Democratic presidencies.

The authors explain that the block method was successful in predicting a justice's vote because it is more realistic than one-dimensional (liberal-conservative) models often assumed in analyzing the judiciary, the authors wrote.

The block model, Guimerà and Sales-Pardo explain, can account for a justice voting with certain justices on issues of federalism, and with others in issues related to civil rights.