Overconfidently conspiratorial: Conspiracy believers are dispositionally overconfident and massively overestimate how much others agree with them

There is a pressing need to understand why people believe in conspiracies. Although past work has focused on needs and motivations, we propose an alternative driver of belief: overconfidence. Across eight studies with 4,181 U.S. adults, conspiracy believers consistently overestimated their performance on numeracy and perception tests (even after taking their actual performance into account). This relationship with overconfidence was robust to controlling for analytic thinking, need for uniqueness, and narcissism, and was strongest for the most fringe conspiracies. We also found that conspiracy believers – particularly overconfident ones – massively overestimated (>4x) how much others agree with them: Although conspiratorial claims were believed by a majority of participants only 12% of the time, believers thought themselves to be in the majority 93% of the time. This was evident even when asked to rate agreement among counter-partisans, indicating that conspiracists are genuinely unaware that their beliefs are on the fringe.