Background:
A jumping-to-conclusions (JTC) bias refers to the gathering of minimal data when making probabilistic judgments and has been associated with delusion formation. Approximately 50% of patients who experience delusions have previously been shown to have a JTC bias. However, the literature is fraught with methodological differences. This study sought to address one of these differences by examining state and trait delusions using large groups of patients with psychosis.
Methods:
Three matched groups (patients with bipolar disorder, patients with schizophrenia and healthy controls) completed the standard beads probabilistic reasoning task and two emotional variants, which examined reasoning using personality and health traits. For each of the three tasks, two probability ratios were used, 85:15 and 60:40. JTC was defined, using the Institute of Psychiatry, London, criteria, as requiring two or less draws. Patients were divided into those with state and trait delusions.
Results:
On the beads 85:15 task, only 4% of patients with schizophrenia and 0% of patients with bipolar disorder showed a JTC bias. The emotional variants produced a similar degree of JTC bias. The 60:40 ratio resulted in an even smaller proportion of JTC. There were no state-trait differences.
Discussion:
Two groups of Australian patients with psychosis (schizophrenia and bipolar disorder) did not show a JTC bias. The authors discuss possible explanations for the discrepancy of these findings with the literature. These include the following: are Australians more indecisive or cautious, how state and trait delusions influence performance, and methodological problems with the task itself.
