May a witness challenge the conviction? (Some) Confirmation bias in legal experts

Abstract

Criminal investigations and trials are always guided by assumptions such that a suspect or defendant has committed a certain crime. Research on confirmation bias suggests that such prior assumptions bias subsequent information processing, fostering a confirmation of those assumptions. Biased information processing, in turn, would pose a severe threat to legal decision-making. Since previous evidence regarding professional decision makers is sparse and inconsistent, the present paper investigated whether legal experts showed evidence of confirmation bias. Specifically, we provided case materials pointing to a certain suspect and investigated evaluations of subsequent eyewitness evidence as a function of whether it was consistent or inconsistent with the initial suspicion. Although identical, witnessing conditions were rated as significantly poorer for inconsistent (vs. consistent) statements, thus, indicating confirmation bias. The effects were rather small, but this finding did not hinge on professional training, as another study with (law) students suggested. We argue that even small effects may threaten fair judgments and that our findings likely underestimate real-world effects.