How Jurors Respond to Expert Testimony in Forensics

Through the National Criminal Justice Reference Service, NIJ has made available a final technical report titled, "Communicating Forensic Science," written by N.J. Schweitzer.

From the abstract:

The purpose of this study was to expand knowledge about how jurors respond to forensic identification expert testimony presented at trial. Researchers pursued this goal by conducting a series of controlled studies involving mock trials and subsequent mock juror deliberations.

The project conducted two different fictitious criminal trials: one, a rape case, and the second an attempted murder case. A sample of laypeople served as “jurors” in each case.

The study found that jurors tend to over-value some attributes of forensic-science expert testimony and under-value other aspects. The most persistent finding is that jurors relied heavily on the “experience” of the testifying expert—including the number of cases in which he or she has appeared—and the expert’s asserted certainty in her/his conclusions.

By contrast, the findings showed that jurors were insensitive to variables indicative of the validity and accuracy of a forensic technique, including testimony about whether or not a technique has been empirically validated and whether evidence is presented to show that the technique is known to produce errors.

Through this research, the author recommends that forensic science organizations and scientific and legal authorities identify standards for the conduct and presentation of expert witness testimony at trial. These standards could inform those with oversight authority and contribute to the training of experts regarding their courtroom presentations, thus ultimately contributing to more meaningful trial presentations and jury decisions.

In addition, courts, legislatures, rules committees, and scientific bodies charged with making policy recommendations might also take into account parts of this research when developing admissibility guidelines for trial judges pertaining to contested identification evidence.

You can download a copy of the report here.

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