The Consistency of Repeated Witness Testimony Leads Triers-of-Fact to Over-Rely on the Power of a Single Voice

Are claims more credible when made by multiple people, or is it the repetition of claims that matters? Some research suggests that claims have more credibility when independent sources make them. Yet, other research suggests that simply repeating information makes it more accessible and encourages reliance on automatic processes—factors known to change people’s judgments. In Experiment 1, subjects took part in a “misinformation” study: Subjects first watched a video of a crime and later read witness reports attributed to one or three different witnesses who made misleading claims in either one report or repeated the same misleading claims across all three reports. In Experiment 2, subjects who had not seen any videos read those same reports and indicated how confident they were that each claim happened in the original event. Subjects were more misled by—and more confident about—claims that were repeated, regardless of how many witnesses made them.  These findings led us to hypothesize that the repeated claims of a single witness are seen as consistent, while the claims of multiple witnesses are seen as having consensus. We tested this hypothesis in Experiments 3 and 4 by asking subjects who had not seen the video to read the reports that repeated the claims. In Experiment 3, half of the subjects read reports that contained some peripheral inconsistencies. In Experiment 4 all subjects read reports that contained inconsistencies, but half of the subjects were warned about the accuracy of the inconsistent reports. Later, everyone indicated how confident they were that each claim really happened. Warning subjects about the inconsistent reports (Experiment 4) led them to rate the repeated claims of a single witness—but not multiple witnesses—as less credible; A finding consistent with our hypothesis.  In Experiment 5, we tested an alternative explanation that a failure to attend to the source of the information may explain our findings by asking half of the subjects to complete a source monitoring component with their confidence test. We failed to find evidence for this explanation.  We conclude that subjects interpreted both the consistency of a single witness's repeated claims, and the consensus among multiple witnesses' converging claims, as markers of accuracy. Importantly, warning subjects about the accuracy of the inconsistent reports reduced subjects’ confidence in the claims made by a single witness, but not multiple witnesses. These findings fit with research showing that repeating information makes it seem more true, and highlight the power of a single repeated voice.