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α: calibrated so average coauthorship-adjusted count equals average raw count
In the United States, Supreme Court justices often vote along ideological lines. Why this is the case remains incompletely understood. To learn more about justices’ preferences and the nature of decision-making in the Court, we differentiate between votes that were pivotal and those that were not. We find that in situations in which a justice is pivotal, her ideology is even more predictive of her vote than usual, especially when her choice matters for unambiguously establishing legal precedent. To interpret this previously unknown pattern in the data, we develop a model of voting in which justices have both expressive and instrumental preferences. That is, the justices strategically trade off which litigant should prevail based on the merits of a case with their desire to shape precedent.