Confirmation bias in witness interviewing: Can interviewers ignore their preconceptions?

Basic research on expectancy effects suggests that investigative interviewers with pre-conceived notions about a crime may negatively influence the interview process in meaningful ways, yet many interviewing protocols recommend that interviewers review all available information prior to conducting their interviews. Previous research suggests that interviewers with no pre-interview knowledge elicit more detailed and accurate accounts than their informed counterparts (Cantlon, et al., 1996; Rivard et al., under review). The current study investigated whether (a) the benefit of blind versus informed interviewing is moderated by cautionary interviewer instructions to avoid suggestive questions and (b) whether any possible effects of pre-interview information extend beyond the immediate context of the forensic interview. ^ Paired participants (N = 584) were assigned randomly either to the role of interviewer or witness. Witnesses viewed a mock crime video and were interviewed one week later by an interviewer who received either correct, incorrect, or no information about the crime event. Half of the interviewers were assigned randomly to receive additional instructions to avoid suggestive questions. All participants returned 1 week after the interview to recall the crime video (for the witness) or the information recalled by the witness during the interview (for the interviewer). All interviews and delayed recall measures were scored for the quantity and accuracy of information reported. ^ Results replicate earlier findings that blind interviewers elicit more information from witnesses, without a decrease in accuracy rate. However instructions to avoid suggestive questions did not moderate the effect of blind versus informed interviewing on witness recall during the interview. Results further demonstrate that the effects of blind versus non-blind interviewing may extend beyond the immediate context of the interview to a later recall attempt. With instructions to avoid suggestive questions, witnesses of blind interviewers were more accurate than witnesses of incorrectly informed interviewers when recalling the event 1 week later. In addition, blind interviewers had more accurate memories for the witnesses' account of the event during the interview compared to non-blind interviewers.^