Conspiracy beliefs are widespread and can have detrimental consequences. As perceived social norms can exert a powerful influence on individuals, we investigated the relationship between perceived conspiracy belief norms and personal endorsement, and whether others’ conspiracy belief is overestimated. In Study 1, UK university students (N = 111) completed measures of their personal conspiracy beliefs and estimations of others’ beliefs (an in-group and an out-group they chose, and a prescribed in-group). Perceived in-groups’ belief strongly predicted personal conspiracy belief; perceived out-group’s belief did not. Studies 2 and 3 replicated these findings in a British community sample (N = 177) and in a UK parent sample (N = 197), focusing on antivaccine conspiracy theories. All studies demonstrated that people overestimate the conspiracy beliefs of others. This is the first demonstration of the association between perceived in-group conspiracy belief social norms and individuals’ personal conspiracy beliefs. Interventions challenging misperceived norms could be effective in reducing conspiracy beliefs.

阴谋论很普遍，可能会产生有害的后果。由于感知社会规范会对个体产生强大的影响，我们调查了感知阴谋信念规范与个人认可之间的关系，以及是否高估了他人的阴谋信念。在研究 1 中，英国大学生 ( N = 111) 完成了对他们个人阴谋信念的测量和对他人信念的估计（他们选择的内群体和外群体，以及规定的内群体）。感知到的群体信仰强烈预测个人阴谋信仰；感知外群体的信念没有。研究 2 和 3 在英国社区样本 ( N = 177) 和英国父母样本 ( N= 197)，专注于反疫苗阴谋论。所有研究都表明，人们高估了他人的阴谋信念。这是第一次证明感知的群体内阴谋信念社会规范与个人个人阴谋信念之间的关联。挑战误解规范的干预措施可以有效减少阴谋论。