Supreme Court Ideology Project

We have made reference to the attitudinal model -- an "external explanation" for what Courts do. This webpage from a couple Standford folk keeps a running tab of justices, relative to other justices.

Supreme Court Ideology Project
Political Science Computational Laboratory
Stanford University

This website uses Bayesian ideal point estimation to update our beliefs about the location of Supreme Court justices. We begin with a prior belief about the location of each justice and update these beliefs after each opinion delivered by the court, learning from the justices' votes what their underlying ideologies are likely to be. Our prior beliefs for Justices Rehnquist, O'Connor, Breyer, Ginsburg, Scalia, Thomas, Kennedy, Stevens and Souter are based on their voting history over the past two years. By contrast, our prior beliefs about the ideologies of Alito and Roberts are somewhat more subjective — based on our knowledge about the President's beliefs and past information about the justices' history and confirmation hearings.

The main questions of interest focus on these new justices and what we can infer about their ideological position relative to the other sitting justices and to the justices they replaced. We are able to obtain estimates of these relative locations as well as estimates of each justice's probability of being the most conservative justice or being, for example, more conservative than the justice he replaced.

The animation on the left side of the page shows the updating process at work. If you don't see a moving picture to the left, you can download Flash here. It plots the posterior density for each justices ideal point — what our belief should be about each justice's location — updating after each vote to the present time.