Competing Models of Judicial Coalition Formation and Case Outcome Determination

Abstract

Forming a coalition on a multi-judge panel involves an inherent trade-off between coalition maximization and ideological outcome optimization. Much scholarship is premised on assumptions about how judges make that trade-off; these assumptions have consequences for how we view and measure judicial decision-making. Specifying these assumptions, formally modeling their effects, and basing measures of judicial behavior on these results offer the potential to improve analysis of judicial decision-making. This article formally explores three commonly posited modes of judicial decision-making: a minimum winning coalition model, representing attitudinalist views of judicial decision-making; a maximum winning coalition, capturing the effect of norms of joint opinion writing and collegiality; and a strategic model, incorporating the concept of the credibility of a marginal justice’s threat to defect from a majority coalition. Each model yields comprehensive predictions of case outcome positions and coalition sizes under given Court compositions; the Rehnquist Court and Roberts Courts are examined here. The models are then operationalized as measures for empirical use. The different impact of the three measures is illustrated by re-running Baird and Jacobi’s analysis of judicial signaling on case outcomes using each measure.