Confirmation Bias in Police Witness Interviews: On the Influence of Prior Information on CBCA Ratings and Credibility Judgments among Criminal Investigators and Law Students

Criteria-Based Content Analysis (CBCA) is the primary instrument used to evaluate the quality of a statement. To date, little research has examined whether CBCA is susceptible to cognitive bias, and existing findings are inconsistent. In this paper, we investigate how prior information about a witness, provided to detectives (Study 1, N = 91) and law students (Study 2, N = 231), influences the perceived content quality of a statement using CBCA, the credibility ratings of the statement and of the victim-witness. Participants watched one of two videos of real witness interrogations regarding an alleged sexual assault by a stranger on the street. The stimulus videos featured either a credible or a non-credible statement. In a 2 × 3 between-subjects design, we examined the effects of prior information about the witness (negative, none, or positive) and video condition (credible vs. non-credible). We hypothesized main effects for both independent variables (prior information and video condition). The results show that both investigators and law students were able to significantly differentiate between the two statements using the CBCA criteria and statement credibility ratings. However, prior information had a significant effect on CBCA scores only in the law student sample. In contrast, CBCA ratings in the investigator sample appeared to be robust against prior information. Judgments of victim-witness credibility, however, were influenced by prior information in both samples. The implications of these findings for criminal investigative practice and professional training are discussed.