If they believe than so shall I: Perceived beliefs of the in-group predict conspiracy theory belief

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 norms of conspiracy beliefs and personal endorsement and whether conspiracy belief amongst others 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 out-group they chose, and a prescribed in-group). The perceived belief of the in-groups strongly predicted personal conspiracy belief; the out-group did not. Study 2 and 3 replicated these findings in a British community sample (n = 177) and a UK parent sample (n = 197) focusing on anti-vaccine conspiracy theories. All studies demonstrated that people overestimate the conspiracy beliefs of others. This is the first demonstration of the association between perceived social norms of in-group conspiracy belief and individuals’ personal conspiracy beliefs. Interventions challenging misperceived norms could be effective in reducing conspiracy beliefs.