Sidebar to the article Uncertainty Ahead: A Shift in How Federal Scientific Experts Can Testify, by Danielle Weiss and Gerald LaPorte, published in NIJ Journal issue no. 279.
Forensic science can be a powerful tool, but there has been limited robust scientific inquiry into how jurors perceive and weigh forensic testimony. To fill this knowledge gap, Arizona State University researcher Nicholas Schweitzer conducted an NIJ-supported study examining the impact of forensic evidence testimony on juror decisions. Schweitzer designed a study of jurors’ reactions to forensic science using three criteria. First, he used juror-eligible participants. Second, Schweitzer videotaped a dramatization of a criminal case but altered three factors of interest: expertise of the forensic expert testifying, admonitions of the jury, and challenges of the forensic expert by the defense counsel. Trial practitioners verified the realism of the case transcripts to ensure that the variables of interest were studied in a realistic courtroom application and would mirror what actual jurors would have to consider. Finally, he focused on the use of non-DNA forensic science in the courtroom, specifically testimony on fingerprint and bite-mark analysis.
After watching the video, the mock jury deliberated on the merits of the case. The deliberations were recorded to assess the impact of the forensic testimony on the jury. Also, each juror was given a survey before and after jury deliberations to capture their attitudes regarding forensic testimony and how these attitudes may have changed after deliberating with their colleagues. Schweitzer used the survey results to gauge the impact of the deliberation process on jurors’ thoughts about forensic science and their decision-making.
Schweitzer conducted three experiments to study different aspects of forensic expert testimony. In the first experiment, he analyzed juror responses to determine if the forensic scientist’s expertise and the validity of the forensic science discipline influenced juror decision-making. Schweitzer found that the forensic scientist’s experience appeared to have more influence on the jurors than the scientific validation of the methods. The experience of the scientist, however, did not seem to affect the jury’s verdict when the mock jury recommended a verdict to acquit or convict the defendant.
The second experiment examined the effect of the forensic expert’s degree of certainty regarding the presence of exculpatory evidence on jurors’ decision-making. Schweitzer found that the mock jurors initially were not swayed by the possibility of exculpatory evidence, but the influence of this potential evidence became greater through the deliberation process. In the post-deliberation survey, the presence of exculpatory evidence was as influential on jury decision-making as the forensic scientist’s experience.
Finally, the third experiment investigated how jurors perceived the forensic expert’s concession that the analysis may include errors. The results were mixed. When the trial involved bite-mark analysis, the concession of potential errors decreased the value of the evidence. However, when the case included fingerprint analysis, the concession increased the perceived credibility of the analysis. Schweitzer concluded that this may be indicative of the jurors’ own a-priori attitudes toward the forensic method being used; fingerprint analysis may have had more credence among jurors prior to their participation in the mock trial.
These findings represent a first step in understanding how jurors perceive forensic testimony, how those initial perceptions change through deliberations, and how those perceptions are ultimately translated into verdicts. A potential limitation of the study is that it focused only on bite-mark and fingerprint analysis. Future research should be conducted to try and replicate these findings with other forensic methods to understand how the type of method used may affect juror impressions of forensic testimony.
About the Authors
Eric Martin is a social science analyst in NIJ’s Office of Research and Evaluation. Angela Moore, Ph.D., is the director of the Justice Systems Research Division in NIJ’s Office of Research and Evaluation.
About This Article
This article was published as part of NIJ Journal issue number 279, published April 2018, as a sidebar to the article Uncertainty Ahead: A Shift in How Federal Scientific Experts Can Testify, by Danielle Weiss and Gerald LaPorte.