How do people estimate the prevalence of beliefs and knowledge among others? Here, we examine the hypothesis that mere repetition of information increases such perceptions of consensus — an “illusory consensus effect.” Although existing evidence suggests that repeated exposure to information may increase its perceived consensus, the impact of repetition has not been tested in isolation from other source and contextual cues. We conducted two experiments to fill in this gap. Prolific participants located in the U.S. read a series of trivia claims — half true and half false in Experiment 1 and all true in Experiment 2. These claims were not attributed to any source. After a short delay, participants made consensus judgments about previously seen (repeated) and new trivia claims. Repetition significantly increased perceived consensus in both experiments; in Experiment 1, participants judged that more Americans would believe repeated (vs. new) information, and in Experiment 2, participants judged that more Americans knew repeated (vs. new) information. These findings provide strong evidence for an illusory consensus effect, such that mere exposure to information increases perceptions of two different measures of consensus: how many others would believe it as well as estimates of current public knowledge. These findings are relevant to our understanding of how our information environments may contribute to (mis)perceptions of consensus.
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