Choosing a short-form measure of conspiracist ideation (i.e., the tendency to believe in conspiracy theories) is fraught. Despite there being numerous scales to choose from, little work has been done to compare their psychometric properties. To address this shortcoming, we compared the internal consistency, 2-week test–retest reliability, criterion validity, and construct validity of five short-form conspiracist ideation measures: the Generic Conspiracist Beliefs Scale–5 (GCB-5), the Conspiracy Mentality Questionnaire (CMQ), the General Measure of Conspiracism (GMC), the American Conspiracy Thinking Scale (ACTS), and the One-Item Conspiracy Measure (1CM). The results of our investigation indicated that all five scales are reliable and valid measures of conspiracist ideation. That said, the GCB-5 tended to perform the best, while the 1CM tended to perform the worst. We conclude our investigation by discussing trade-offs among the five scales, as well as providing recommendations for future research.
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