Measuring conspiracy beliefs among Democrats and Republicans: A test of the measurement invariance of four short-form conspiracist ideation scales

Are Republicans more likely to believe in conspiracy theories than Democrats? This question has received considerable attention among researchers, but answering it requires measures of conspiracist belief that function the same among Democrats and Republicans. Unfortunately, evidence of such measurement invariance is scarce. To address this limitation, the current preregistered study tested the invariance of four short-form conspiracist ideation measures across the two major US political parties. We hypothesized that all four scales would achieve strict factorial invariance. The General Measure of Conspiracism was the only measure to reach this level. The Generic Conspiracist Beliefs Scale–5 and Conspiracy Mentality Questionnaire, by contrast, only achieved metric invariance, despite the former demonstrating the greatest overall fit of the measures tested. The American Conspiracy Thinking Scale only achieved configural invariance. Researchers who are interested in comparing conspiracist ideation between Democrats and Republicans may, therefore, be best served by using the General Measure of Conspiracism.