The effectiveness of opposing expert witnesses for educating jurors about unreliable expert evidence.

We tested whether an opposing expert is an effective method of educating jurors about scientific validity by manipulating the methodological quality of defense expert testimony and the type of opposing prosecution expert testimony (none, standard, addresses the other expert's methodology) within the context of a written trial transcript. The presence of opposing expert testimony caused jurors to be skeptical of all expert testimony rather than sensitizing them to flaws in the other expert's testimony. Jurors rendered more guilty verdicts when they heard opposing expert testimony than when opposing expert testimony was absent, regardless of whether the opposing testimony addressed the methodology of the original expert or the validity of the original expert's testimony. Thus, contrary to the assumptions in the Supreme Court's decision in Daubert, opposing expert testimony may not be an effective safeguard against junk science in the courtroom.