Empirical studies of collegial courts typically analyze the dispositional votes of judges. Theoretical models of collegial courts, by contrast, typically assume that judges care about, and choose, policies. In this paper, we use data on the behavior of justices of the Supreme Court of the United States (from the Spaeth Supreme Court Database, 1953-2008) to show that this discrepancy is not innocuous: dispositional votes are different from policy choices, and that difference has implications for understanding the doctrine the Court produces. We present evidence that disposition coalitions differ from policy coalitions in a significant number of cases, and argue they differ along ideological lines. For this reason, we claim dispositional votes are not an adequate proxy for policy choice.

Our preliminary analysis establishes two other claims. First, we show that within a natural court, policy coalitions are diverse rather than homogeneous. Second, we present evidence that the ideological content of opinions moves in tandem with the ideological makeup of the policy coalition supporting the majority opinion.