Prentice, R. A. & Koehler, J. J. (2003). A Normality Bias in Legal Decision Making. Cornell Law Review, 88, 583-650.

ABSTRACT

Few aspects of our legal world are more important than understanding how legal fact finders determine causation and assign blame. Yet this process is poorly understood. Contrary to the assumptions of law-and-economics scholars, decision makers, including judges and jurors, do not reason as homo economicus. Among the many factors that affect decision makers are an omission bias (a tendency to blame actions that produce bad results more than inactions [omissions] that produce bad results) and a normality bias (a tendency for people to react more strongly to bad outcomes that spring from abnormal circumstances than to otherwise identical outcomes that spring from more ordinary circumstances). Traditional economic theory has no explanation for these and other psychological biases. This article draws from a substantial behavioral literature to study their origins, effects, and implications for the rule of law. We argue, among other points, that the omission bias may explain the legal system’s failure to impose a duty to rescue, and that the normality bias helps explain the common law’s approach to causation and punishment.

The omission and normality biases reinforce one another when inaction preserves the normal state and when action creates an abnormal state. This common state of affairs pushes the law and the legal system in a conservative direction, where failures to act go unchallenged or unpunished, and deviations from norms are discouraged or punished relatively severely. But what happens when the two biases push in opposite directions as they would when inaction promotes an abnormal state or when action promotes a normal state? Which bias exerts the stronger influence on the judgments and behavior of legal decision makers?

In two controlled experiments, one involving medical malpractice and the other stockbroker negligence, we address this issue. We find that jurors asked to assign responsibility and award damages pay much more attention to the normality of conditions than to whether those conditions arose through acts or omissions. Defendants who followed a nontraditional medical treatment regime or who chose a nontraditional stock portfolio were blamed and punished more strongly for bad results than defendants who obtained equally poor results when recommending traditional medical regimes and stock portfolios. Whether these choices arose through action or omission was essentially irrelevant.

We trace the central role that beliefs about normality and abnormality play in legal contexts to the doctrine of social proof (the tendency to take behavioral cues from the actions of others), and discuss the implications of a robust normality bias for American jurisprudence.