We quantify the extent to which Supreme Court justices learn from each other. We analyze conference votes, which are cast behind closed doors in order of seniority. We provide causal evidence that junior justices systematically incorporate the votes of their senior colleagues. To explain this evidence, we augment existing theories of judicial decision making by introducing social learning into a structural model of sequential voting in the Court. In our model, justices make decisions under incomplete information and incorporate their preferences, public and private information, and the choices of previous justices in the voting sequence. We show that the information contained in the voting history affects the outcome of the Court in 18% of cases. We compute the effect of the seniority rule on the quality of Supreme Court’s rulings and compare it to alternative voting mechanisms.

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