Psychological Science 1–9 © The Author(s) 2015 Reprints and permissions: sagepub.com/journalsPermissions.nav DOI: 10.1177/0956797615598740 pss.sagepub.com Research Article Immediately after the Charlie Hebdo murders on January 7, 2015, in Paris, amateur theories purportedly explaining the events began to flourish online. Such fast and wide- spread hypotheses after major events are now familiar and are known as conspiracy theories, defined as unveri- fied claims of conspiracy (i.e., a secret agreement between powerful individuals to enforce and hide a malevolent agenda) with sensationalistic implications (e.g., Douglas & Sutton, 2008). Conspiracy theories typically involve interpreting errant data (Keeley, 1999), that is, unaccounted-for ele- ments in the official narrative, as evidence of a conspir- acy rather than mere anomalies. In the Charlie Hebdo case, the errant data were, for example, discrepancies in different pictures of the offenders’ car or the fact that one perpetrator left his ID card in the car. This highlighting of alleged incongruities is sometimes summarized by the expression “nothing happens by accident” and has been outlined as a critical mechanism of conspiracist ideation (Barkun, 2003; Campion-Vincent, 2005; Lewandowsky et al., 2015; Taguieff, 2013). In a similar vein, McCauley and Jacques (1979), as well as Leman and Cinnirella (2007), suggested that the common heuristic that big events have big causes may lead to conspiracy thinking, which indicates that major events that are targeted by conspiracy theories are not intuitively attributed to minor causes, such as chance. Early social and psychological mechanisms for con- spiracist ideation involved the role of nonclinical 598740PSS XX X 10.1177/0956797615598740Dieguez et al.Conspiracist Ideation and Randomness Perception research-article 2015 Corresponding Author: Sebastian Dieguez, Department of Medicine, University of Fribourg, Ch. du Musée 5, 1700 Fribourg, Switzerland E-mail: sebastian.dieguez@unifr.ch Nothing Happens by Accident, or Does It? A Low Prior for Randomness Does Not Explain Belief in Conspiracy Theories Sebastian Dieguez 1 , Pascal Wagner-Egger 2 , and Nicolas Gauvrit 3,4 1 Laboratory for Cognitive and Neurological Sciences, Department of Medicine, University of Fribourg; 2 Department of Psychology, University of Fribourg; 3 Human and Artificial Cognition Laboratory, University of Paris-Saint-Denis; and 4 Department of Life Science, École Pratique des Hautes Études Abstract Belief in conspiracy theories has often been associated with a biased perception of randomness, akin to a nothing- happens-by-accident heuristic. Indeed, a low prior for randomness (i.e., believing that randomness is a priori unlikely) could plausibly explain the tendency to believe that a planned deception lies behind many events, as well as the tendency to perceive meaningful information in scattered and irrelevant details; both of these tendencies are traits diagnostic of conspiracist ideation. In three studies, we investigated this hypothesis and failed to find the predicted association between low prior for randomness and conspiracist ideation, even when randomness was explicitly opposed to malevolent human intervention. Conspiracy believers’ and nonbelievers’ perceptions of randomness were not only indistinguishable from each other but also accurate compared with the normative view arising from the algorithmic information framework. Thus, the motto “nothing happens by accident,” taken at face value, does not explain belief in conspiracy theories. Keywords conspiracist ideation, subjective randomness, algorithmic complexity, conspiracy theories, beliefs Received 4/8/15; Revision accepted 7/13/15 Psychological Science OnlineFirst, published on September 21, 2015 as doi:10.1177/0956797615598740 at Universite de Fribourg on September 23, 2015 pss.sagepub.com Downloaded from