Path Dependency in Jury Decision Making

A large behavioral economics literature is concerned with cognitive biases in individual and group decisions, including sequential decisions. These studies often find a negative path-dependency consistent with mechanisms such as the gambler's fallacy or contrast effects. We provide the first test for such biases in group decision making using observational data. Specifically, we study more than 27,000 verdicts adjudicated sequentially by over 900 juries for high-stake criminal cases at London's Old Bailey Criminal Court in the 18th and 19th centuries. Using jury fixed effects to account for heterogeneity in their baseline propensity to convict, we find that a previous guilty verdict significantly increases the chance of a subsequent guilty verdict by 6.7%–14.1%. This positive autocorrelation is robust to alternative estimation strategies, independent of jury experience and driven by the most recent lag and pairs of similar cases. Such positive path dependency may be explained by sequential assimilation effects, which may reflect a jury's desire to be internally consistent, and short-term “emotional” impacts of the characteristics and/or outcome of one case on another. As in modern-day jury studies, our results highlight that factors independent of the facts and evidence of the current case might affect jury behavior.