THE GATEKEEPER EFFECT: The Impact of Judges' Admissibility Decisions on the Persuasiveness of Expert Testimony

In a pair of mock-trial studies of a possible "gatekeeper" effect, our participants were presented with a summary of a trial that included a piece of expert scientific evidence. The judge's decision was manipulated to admit the scientific evidence, as well as the quality of the evidence and the credibility of the expert. Participants were found to be less critical of and more persuaded by expert evidence when it was presented within a trial, compared with the same evidence presented outside of a courtroom context. These findings suggest that, when judges allow expert testimony to reach the jury although the evidence is of low quality, they imbue it with undeserved credibility. Furthermore, no changes in participants' perceptions of the evidence were found if the mock jurors were explicitly informed that the judge had evaluated the evidence, suggesting that the participants assumed that judges normally review evidence before allowing it to reach the jury. In addition, implications for basic research are discussed, as the moderating effects of a gatekeeper have not previously been considered by established models of persuasion.