Measuring Belief in Conspiracy Theories: Validation of a French and English Single-Item Scale

We designed, in French and in English, a single-item scale to measure people’s general tendency to believe in conspiracy theories. The validity and reliability of this scale was assessed in 3 studies (total N = 555). In Study 1 (N = 152), positive correlations between the single-item scale and 3 other conspiracy belief scales on a French student sample suggested good concurrent validity. In Study 2 (N = 292), we replicated these results on a larger and more heterogeneous Internet American sample. Moreover, the scale showed good predictive validity—responses predicted participants’ willingness to receive a bi-monthly newsletter about alleged conspiracy theories. Finally, in Study 3 (N = 111), we observed good test-retest reliability and demonstrated both convergent and discriminant validity of the single-item scale. Overall these results suggest that the single-item conspiracy belief scale has good validity and reliability and may be used to measure conspiracy belief in favor of lengthier existing scales. In addition, the validation of the single-item scale led us to develop and start validating French versions of the Generic Conspiracist Beliefs scale, the Conspiracy Mentality Questionnaire, and a 10-item version (instead of the 15-item original version) of the Belief in Conspiracy Theories Inventory.