A new paradigm to measure probabilistic reasoning and a possible answer to the question why psychosis-prone individuals jump to conclusions.

Abstract

Jumping to conclusions (JTC) distinguishes patients with schizophrenia from both healthy and psychiatric controls. JTC is typically assessed using the beads task, which, however, faces a number of limitations as to its interpretability and reliability. The present study set out to validate a new paradigm to assess JTC: the box task. We adopted a psychometric psychosis proneness approach and divided a large population sample into participants who scored high versus low on a scale tapping psychosis-like experiences. Participants performed a variant of the original beads task along with a new JTC task, the box task, with or without time pressure. The box task requires participants to infer which of two ball colors will be more prevalent in a matrix of boxes. The box task and the beads task were significantly correlated at a medium effect size, thus demonstrating criterion validity for the box task. As hypothesized, participants who scored high on psychosis-like experiences showed particularly strong JTC and a decreased decision threshold relative to low scorers, especially in the box task version with time pressure; in contrast, group differences in the beads tasks only achieved trend-wise significance. Mediation analyses showed that fewer draws to decisions were predicted by either a lower decision threshold or by higher initial probability estimates for the dominant item. The study establishes the criterion and construct validity of a new JTC task. Its advantages over the traditional beads task are better comprehensibility and usability; multiple parallel versions can be created thus raising reliability. (PsycINFO Database Record