Paranormal belief and susceptibility to the conjunction fallacy

Numerous studies have shown paranormal believers misperceive randomness and are poor at judging probability. Despite the obvious relevance to many types of alleged paranormal phenomena, no one has examined whether believers are more susceptible to the ‘conjunction fallacy’; that is to misperceiving co-occurring (conjunct) events as being more likely than singular (constituent) events alone. The present study examines believer vs. non-believer differences in conjunction errors for both paranormal and non-paranormal events presented as either a probability or a frequency estimation task. As expected, believers made more conjunction errors than non-believers. This was true for both event types, with both groups making fewer errors for paranormal than for non-paranormal events. Surprisingly, the response format (probability vs. frequency) had little impact. Results are discussed in relation to paranormal believers’ susceptibility to the conjunction fallacy and more generally, to their propensity for probabilistic reasoning biases.