Dateline: February, 2007, Issue 6

How important to jurors are the credentials of expert witnesses?

Jurors do not always distinguish between highly qualified and less qualified experts, even when the difference in these experts' credentials is brought to their attention.

Research by Cooper and colleagues (1996) looked at how the credentials of expert witnesses affect their persuasiveness. Jurors were shown a videotape of a trial in which two scientists provided evidence on whether PCBs could have caused a plaintiff's illness. Unbeknownst to different groups of jurors, four different versions of the videotape existed varying in the complexity of the evidence discussed and the credentials of the experts testifying. Jurors saw only one of the videotapes, where one of the expert's credentials were either strong or weak and the evidence discussed was either highly complex or less complex.

Jurors were more persuaded by a highly expert witness than by a less expert witness, but only when the evidence was highly complex. When evidence is complex, jurors are more persuaded by an expert witness with strong credentials. When evidence is less complex, jurors rely primarily on the content of the testimony, and the expert's credentials have little impact on the persuasiveness of the testimony. Said differently, when evidence is not complex, jurors focus on what experts say, rather than on their credentials.

Source Cooper, J., Bennett, E. A., & Sukel, H. L. (1996). Complex scientific testimony: How do jurors make decisions? Law and Human Behavior, 20, 379-394.