A comparison of reasoning styles between actively delusional and delusion-prone individuals

Previous research has demonstrated a reasoning bias in actively delusional people in which they accept hypotheses that are too improbable to be accepted by people without delusions (McGuire et al., 2001). The current study sought to extend these findings by investigating whether a similar reasoning bias is evident in an at-risk or delusion-prone population. Participants from the Hofstra undergraduate population were identified as either control or delusion-prone based on their responses to the Peters et al. Delusions Inventory (PDI) - 21 Item. Their performance on a probabilistic reasoning task was then compared to actively delusional inpatients recruited from Bellevue Hospital. The reasoning task involved evaluating narratives of actual delusional belief statements and neutral belief statements and estimating the probability that the event being described could actually take place or be true. It was hypothesized that the delusion-prone and actively delusional participants would assign significantly higher probabilities to delusional narratives than the control group. It was further hypothesized that all three groups would reason similarly about the neutral belief statements. Familiarity with the content of the delusional narratives was also measured, as past research has identified this variable as possibly related to biases in reasoning. It was expected that the proposed reasoning bias in actively delusional and high delusion-prone participants would not be fully explained by the degree of familiarity with the content of the delusional narratives. Results partially supported the hypotheses. While the actively delusional group did accept hypotheses too improbable for the control group to accept, the same was not true for the delusion-prone group. Although the delusion-prone group generally assigned higher probabilities to delusional narratives, the difference was not significant. Familiarity was found to be a mediator in the relationship between delusional group status and higher probability estimates on delusional narratives. In regard to neutral narratives, actively delusional participants reasoned less accurately than the delusion-prone and control groups.