Assessing How Fact-Checks Influence Accuracy and Consensus Judgments: Evidence From the Olympics.

Fact-checks have become a popular intervention aimed at tackling misinformation, yet concern has persisted related to the potential for fact-checking to inadvertently amplify false narratives-a phenomenon commonly referred to as a "backfire effect." At the same time, recent evidence from research on repeated claims has suggested that there is a risk that fact-checks may also generate misperceptions regarding societal beliefs-or an "illusory consensus" effect. This paper presents findings from an ecologically valid two-wave experimental study that tested whether repeated fact-checking interventions could cause either of these negative outcomes. To further enhance the validity of the design, we draw on quota-balanced samples of participants from the United States, France, and South Africa (N = 680), who were presented with a set of true and false posts taken from online discussions regarding the 2024 Summer Olympic Games in Paris, France. Outcome measures focused on personal accuracy judgments (i.e., how accurate participants deemed each claim) and consensus estimates (i.e., whether their fellow citizens would believe each claim). After the Olympics concluded, participants were asked to assess both new and previously reviewed statements. Consistent with prior work, results indicate no evidence of the backfire effect ( d $d$  = 0.048). The findings also provide evidence of a small "illusory consensus" effect ( d $d$  = 0.125), whereby participants who had previously seen fact-checks were more likely to estimate that the wider population would accept these debunked claims as accurate. Supplementary analyses of true statements reveal that fact-checks produced large, durable improvements in accuracy judgments ( d $d$  = 0.71-0.91), suggesting that fact-checking was substantially more effective at reinforcing correct beliefs than it was at generating unintended consequences. Item-level analyses further reveal heterogeneity across misinformation narratives, indicating that the specific content of false claims may moderate both the persistence of corrections and consensus distortions. Implications for fact-checking strategies and public perceptions of misinformation, including the need for further studies which incorporate group dynamics, are discussed and debated.