The Analysis of Competing Hypotheses in Legal Proceedings

ABSTRACT The present study examined the potential benefit of the Analysis of Competing Hypotheses (ACH) method to reduce confirmation bias in legal proceedings. To this end, 222 law students participated in an online study and assessed an ambiguous homicide investigation. Participants were divided into three groups: control group, single‐hypothesis group, and ACH group. To assess the test–retest reliability of the ACH method, a follow‐up study with 30 participants was conducted. As no indication of confirmation bias was observed, the possible benefits of the ACH method as a debiasing method in legal proceedings could not be fully assessed. However, participants' confidence in their guilt assessment significantly increased when applying the ACH method. Simultaneously, exclusively examining the guilt‐hypothesis led to a focus on significantly more non‐diagnostic evidence. No other group differences emerged. Findings regarding the ACH method's temporal stability are mixed, highlighting the method's sensitivity to small changes in the evaluation process.