Persuasion Factors that Influence the Effectiveness of Cross-Examination of a Forensic Expert
False and misleading forensic testimony is a large contributor to wrongful convictions. Many forensic science disciplines are subjective and have concerning error rates, and forensic experts often testify with unfounded certainty regarding their analyses. These issues, coupled with jurors' misbeliefs about forensic science, result in criminal convictions despite weak evidence against a defendant. A possible safeguard against false and misleading forensic testimony is cross-examination of a forensic expert. Some cross-examination research suggests that particular types of questioning of an expert witness effectively reduce jurors' perceptions of the expert's credibility. Research has identified factors that influence the persuasiveness of expert witnesses. Specifically, Martire and colleagues (2020) created an Expert Persuasion Expectancy Framework that includes eight factors that influence expert persuasiveness. Two of these factors, field and trustworthiness, serve as cues that affect the credibility of the message source (i.e., expert witness). Two other factors, foundation and consistency, serve as message credibility cues (i.e., testimony content). Because source credibility and message credibility are factors that affect persuasion, manipulating these four factors in an expert witness should influence the perceived credibility of the expert and the perceived credibility of the expert's message - and ultimately affect the persuasiveness of the expert testimony. The current study tested whether highlighting four of Martire's factors (i.e., consistency, field, foundation, and trustworthiness) in a cross-examination of a forensic expert effectively reduces the persuasiveness of the expert. The current study also tested individual differences (i.e., Need for Cognition, legal authoritarianism, attitudes toward the legal system, attitudes toward forensic science, and legal fiction consumption) as potential moderators of the framework. A total of 563 mock jurors read a trial summary that included a crime description of an aggravated robbery in which the perpetrator left fingerprints at the crime scene, a direct examination of the prosecution's fingerprint analyst who testified that the latent prints match the defendant's, and one version of a cross-examination of the fingerprint expert by the defense attorney. For the cross-examination, participants read a transcript in which the defense attorney questioned the forensic expert on his testimony. Sixteen different versions of the cross-examination manipulated the expert's consistency, field, foundation, and/or trustworthiness. The cross-examination for each condition contained the presence (i.e., manipulation) or absence (i.e., control) of questions that reduced the consistency, field, foundation, and trustworthiness of the expert. After the cross-examination, participants indicated how guilty they believed the defendant was, completed source and message credibility scales, and completed individual difference measures. Results indicated that perceptions of the forensic expert's field, trustworthiness, consistency, and foundation positively predicted message credibility and field, trustworthiness, and foundation positively predicted expert credibility. Expert and message credibility also predicted guilt ratings. Further, some of these relationships were moderated by attitudes toward forensic science and authoritar¬ianism. Although other individual differences such as Need for Cognition and legal system attitudes did not moderate any of the above relationships, these individual differences did directly affect guilt ratings. These findings have several implications for the legal system. Defense attorneys can use the study's findings to construct effective cross-examinations of forensic experts. Findings also indicate which individual differences should be considered during jury selection due to their influence on the processing of trial information and evidence. The study's findings also synthesize the credibility and persuasion literature.
Cross-examination, Expert credibility, Expert persuasion, Expert testimony, Forensic expert, Jury decision making
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