The Relationship Between Cognitive Biases and Delusional Beliefs Across the Psychosis Continuum

Author: Benjamin McLean

McLean, Benjamin, 2018 The Relationship Between Cognitive Biases and Delusional Beliefs Across the Psychosis Continuum, Flinders University, College of Education, Psychology and Social Work

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The Jumping to Conclusions (JTC) and evidence-integration biases have been found to be associated with delusions in schizophrenia, and are proposed to contribute to delusion formation and maintenance. Past meta-analyses had tested the relationship between JTC and delusions in psychosis groups, but the use of groups with mixed diagnoses made it unclear whether the association was between JTC and delusions, consistent with a causal role for biases, or between JTC and schizophrenia only. The evidence-integration biases had not been meta-analytically tested. This thesis determined by meta-analysis that the JTC and evidence-integration biases covary with the presence and absence of delusions in schizophrenia, and that JTC is associated with delusions in disorders other than schizophrenia, consistent with the causal account (Study 1). Nevertheless, significant heterogeneity in this and previous meta-analyses indicated potential problems with the most common means of identifying JTC, namely the beads task. Hence this research conducted the first formal assessment of the reliability of the beads task using multiple trials, and tested a new, modified version of the task that incorporates distractor sequences (Study 2). The traditional beads task was shown to have inadequate reliability, but the new task had significantly better reliability. Given the greater reliability of the new beads task, the relationship between it and delusion-proneness in non-clinical samples was reassessed (Studies 3 and 4). Contrary to what was expected from both the clinical and non-clinical literature, in two independent samples, delusion-proneness was associated with less JTC on the new task. A possible mechanism for this of higher odds literacy leading to both reduced delusion-proneness and increased apparent JTC was tested (Study 4), but was found not to account for this relationship. Preliminary data indicated that an alternative mechanism of generalised anxiety and risk-aversion driving increased delusion-proneness and information-gathering might account for this relationship, but requires further proof. Ultimately, testing the new task for convergent validity, and in clinical populations where the JTC-to-delusions relationship is more robust, will be necessary to verify that the new beads task measures data-gathering and identifies JTC as intended. This thesis adds to our knowledge of the relationship between cognitive biases and delusions by clarifying the nature of this relationship in clinical samples, by identifying some of the psychometric limitations of the current beads task, and by developing a more reliable alternative task.

Keywords: psychosis, schizophrenia, delusions, cognitive bias, jumping to conclusions, JTC, bias against disconfirmatory evidence, BADE, beads task, repeatability, reliability

Subject: Psychology thesis

Thesis type: Doctor of Philosophy
Completed: 2018
School: College of Education, Psychology and Social Work
Supervisor: Dr Julie Mattiske