## FantasySCOTUS.net Predictions of the 10th Justice: Predicting Justices in the Majority and Probable Coalitions

January 15th, 2010

Welcome to the sixth installment of Predictions of the 10th Justice, brought to you by FantasySCOTUS.net. The league has over 3,400 members, who have made predictions on all cases currently pending before the Supreme Court.

By conducting a rigorous statistical analysis of 26 of the most hotly contested cases this terms, we have developed a descriptive model to elucidate how frequently a Justice will vote in the majority, and how this impacts the building of majority coalitions on the Court. Additionally, these statistics paint a picture of how Justice Sotomayor, the newest addition to the Court, will vote, and which coalitions she will join. Finally, this analysis aims to answer the elusive question, of how often Justice Kennedy will be in the majority.

We first calculated the percentage of predictions placing each Justice in the majority. While this method overlooks whether the Court will affirm or reverse the lower court, it does serve as an indicator for which Justices are better forming coalition. Specifically, for the 26 cases we considered, we calculated four data points for each Justice.

1. Minimum- The case where the lowest percentage of predictions placed that Justice in the Majority
2. Maximum- The case where the highest percentage of predictions placed that Justice in the Majority
3. Media- The middle prediction (50% above, and 50% below) that placed the Justice in the Majority
4. Mean- The average prediction that placed the Justice in the Majority.

Predictions, of the 10th Justice, after the jump.

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Our analysis for Justice Sotomayor reveals:

1.  Minimum- in Citizens United, the Hillary Movie campaign finance reform case, only 29% of the predictions placed Justice Sotomayor in the majority. Of all 26 cases, this is the case where Sotomayor is least likely to vote in the majority.

2. Maximum- in Bilksi v. Kappos, 83% of the predictions placed Justice Sotomayor in the majority. Of the 26 cases we considered, this is the case where Sotomayor is most likely to vote in the majority.

3. Median- Of the 26 cases we considered, Sotomayor was more likely than 63% to be in the majority in half of the cases.

4. Mean- On average, Sotomayor will have a 61% (predicted) chance of being in the majority for a case.

Further analysis shows Justices Sotomayor, Ginsburg, and Breyer each has the same minimum probability (.29) of being in the majority for a case. Each of the four liberal justices is least likely to be in the majority opinion in Citizens United, the Hillary Movie campaign finance reform case. This matches our previous predictions regarding Citizens United, where we predicted that Chief Justice Roberts, and Justices Scalia, Kennedy, Thomas, Alito were likely to be in the majority.

Our analysis also shows that for Chief Justice Roberts, as well as Justices Stevens, Kennedy, Alito, and Breyer, their median is equal to their mean. This indicates that the odds of the Justice voting in the majority is smoothly distributed across cases. This fact signifies that they have less variation in odds for being in the majority for a single case.

As the box-plot shows, Justice Kennedy, as expected, has a very tight distribution with a high median score. This reflects the fact that he is likely to be the deciding vote. However, he is still far short of a 100% prediction; so there is no certainty how he will vote. We generally predict that Justice Kennedy will be in the majority most of the time.

Justice Sotomayor, as the newest Justice, has the widest distribution. This is to be expected in predictions since this is her first term and her judicial position is not yet fully understood. We have a less precise of an idea when Sotomayor will be in the majority. Stevens has the next widest distribution, indicating that he is also quite unpredictable.

Justices Ginsburg and Breyer are interesting, because they have relatively close minimums, maximums, and medians. However, Justice Ginsburg’s median is centered slightly lower, possibly indicating that Ginsburg is more likely to dissent than Breyer, because she is less likely to be in the majority.

Comparatively speaking, Roberts, Scalia, Alito, and Thomas have tighter distributions than the other Justices (except Kennedy) and are generally considered more likely to be in the majority together as a coalition. Among this grouping, Thomas is more likely to defect and dissent.

Many thanks to Corey Carpenter for his stellar research assistance with this post.