Can 'gatekeeper effect' bolster weak opinions?

The much ballyhooed Daubert decision of 1993 was intended to minimize the effect of so-called "junk science" in the courtroom. ("Junk science," by the way, was a term popularized by the book Galileo's Revenge, part of an orchestrated corporate attack on class action litigation, but that's a story for another day.) But Daubert may be having a paradoxical effect instead, of lending greater credibility to expert witness opinions.

That is the premise of the lead article in Psychology, Public Policy and Law, by Nick Schweitzer and Michael J. Saks of the Law and Social Psychology Research Group at Arizona State University.

The "gatekeeper effect" is the label being given to this phenomenon, of jurors giving extra weight to scientific evidence just because it has been vetted by judges.

Remember that formal rules of evidence are aimed at excluding improper evidence from jurors' consideration. And under the U.S. Supreme Court's ruling in Daubert, judges have become more and more responsible for filtering evidence prior to its admission.

Two experiments tested whether mock jurors (as usual, university undergrads rather than real-life jurors or eligible jurors) were more persuaded by evidence when they thought a judge had filtered it. The findings: A key predictor of how much stock the jurors put in scientific evidence was whether they thought a judge had deemed it acceptable.

Why is this potentially problematic? Judges, as many of us know, are not always well prepared to serve as filterers of scientific evidence. Some of them do not do it well. Also, in many jurisdictions, Daubert is not the law, so jurors may be assuming incorrectly that the evidence they hear has passed through a filtering system.

Concludes the article, "When judges allow expert testimony to reach the jury, they are implicitly lending credence to the testimony, increasing its persuasiveness. This tips the scales toward the party offering the expert witness, perhaps affecting the jury's verdict. Ironically, a landmark Supreme Court decision motivated in large part by a desire to shield jurors from 'junk science' could serve to heighten the impact of false or misleading scientific evidence when judges allow it through the courtroom gates."

I find it a bit troubling that jurors may be persuaded by expert testimony that is false, misleading, or scientifically weak, based on incorrect assumptions about the process. I don't, however, find it too terribly surprising.

The article, "The gatekeeper effect: The impact of judges' admissibility decisions on the persuasiveness of expert testimony," is available upon request from lead author N.J. Schweitzer.

Thursday, May 28, 2009