Prior experimental studies suggest that judges are susceptible to cognitive biases when making legal decisions, such as being motivated by the legally irrelevant nature of a defendant’s crime when determining the admissibility of challenged evidence. However, that research has been constrained to hypothetical cases, limiting the real-world conclusions that can be drawn from it. Addressing this empirical gap, we offer a novel observational analysis that tests the influence of crime severity on suppression outcomes in actual search-and-seizure cases from U.S. Courts of Appeals.
Using legislative criminal penalties to measure crime severity, our analysis shows that as crime severity increases, judges become significantly less likely to exclude challenged evidence on Fourth Amendment grounds—even though crime severity is not a doctrinally relevant consideration. Another legally extrinsic factor, the ideology of the opinion-writing judge, is also found to exert an influence, but only in the most serious criminal cases that involve a life sentence or the death penalty. In these particularly high-stakes decisions, conservative-leaning judges are more likely to uphold the admissibility of challenged evidence, while liberal-leaning judges are more likely to suppress it. Our data also indicate that the intrusiveness of the challenged police search, a doctrinally relevant factor, independently influences admissibility judgments.
The results of our study both confirm and complicate existing understandings of judicial decision-making in the Fourth Amendment context and beyond. Furthermore, by directly building on two lines of prior experimental findings grounded in psychology theory, the “empirical triangulation” approach we operationalize here illustrates an advantageous model for optimizing the validity of empirical scholarship on judicial behavior.