Zeal Spillovers: The Adversarial Bias in Simulated Pre-Trial Decision Making

The adversarial legal procedure is one of the defining characteristics of Anglo-American law. Adversarialism is lauded for its capacity to discover the factual truth, which is said to be revealed by the clash between zealous advocates. This study further explores the proposition that adversarial contests trigger a bias that pervades adversarial actors’ judgments, beliefs, motivations, and emotions, and thus skews how they perceive and approach their cases. Specifically, we set out to extend prior research by testing whether the adversarial bias could spill over to skew simulated pre-trail prosecutorial tasks: the decision to seek an indictment and forming judgments in advance of the plea negotiation. In a simulation with lay people, we find that the adversarial bias does indeed skew pre-trial decisions. This result is troubling because the epistemic justification of adversarialism has little to contribute to these decisions, as indictment decisions are made unilaterally by prosecutors, and plea negotiations take place under heavily lopsided power and access to information. It follows that while adversarial zeal has little to contribute to pre-trial decisions, it can readily infest them with zeal. While ecological validity considerations abound, this study demonstrates the psychological plausibility that the adversarial bias results in heightened levels of indictment and stiffer punishments, thus highlighting prosecutors’ potential contribution to the exceptionally high rate of people sent to prison in the US.