The role of confirmation bias in suspect interviews: A systematic evaluation

Purpose. The three studies presented in this paper systematically examined the effect of expectations of guilt on interviewer questioning style, confession, denial rates, and suspects' verbal behaviour during interview. Method. Undergraduate students were recruited to participate in the three studies. In Study 1, 61 participants formulated questions that they wanted to ask a suspect to determine whether or not they cheated on a task. Prior to formulating their questions, participants were led to believe that the suspect was likely to be guilty or innocent. In Study 2, 45 ‘innocent’ and ‘guilty’ participants were accused of cheating on a task and were interviewed with either guilt‐presumptive questions or neutral questions. In the final study, 58 participants listened to a selection of audiotaped interviews from Study 2. They then rated various aspects of the suspects' verbal behaviour. Results. As hypothesized expectations of guilt resulted in the formulation of more guilt‐presumptive questions even when participants were free to generate their own questions (Study 1). A significant association was found between suspect guilt/innocence and whether they confessed or denied, although there was no association between questioning style and confession or denial rates (Study 2). However, as expected, ratings of independent observers who listened to tape recordings of the suspect interviews indicated an influence of questioning style on the suspects' verbal behaviour whereby a self‐fulfilling prophecy effect occurred (Study 3). Conclusions. These results indicate that expectations of guilt can indeed have an effect on questioning style and that this in‐turn can lead to a self‐fulfilling prophecy effect.