To Believe or Not to Believe in Conspiracy Claims? That Is a Question for Signal Detection Theory.

Conspiracy mentality is conceptualized as a continuum. Research on this topic has focused on unwarranted conspiracy claims and the upper end of the conspiracy-mentality continuum-people seeing conspiracies everywhere. This focus neglects warranted conspiracy claims and the lower end of the continuum. To better understand conspiracy mentality, we aimed to clarify both ends of the continuum using signal detection theory. We examined how people evaluate warranted and unwarranted conspiracy claims across levels of conspiracy mentality in two studies with 331 French-speaking adult participants from France, Switzerland, and Belgium (Study 1) and 576 English-speaking adult participants from the United States and the United Kingdom (Study 2), both groups recruited via Prolific. Compared with participants high in conspiracy mentality, those low in conspiracy mentality not only believed less in conspiracies but also underestimated their prevalence. However, participants low in conspiracy mentality were more accurate at distinguishing warranted from unwarranted conspiracy claims. These results provide a better understanding of conspiracy mentality and its relationship with the perceived truthfulness of conspiracies.