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Abstract
Rumination, worry, post-event processing and similar constructs have been recently grouped under the broader transdiagnostic concept of repetitive thought. Repetitive thought has been implicated as a maintaining factor across a broad range of disorders (such as depression, generalised anxiety disorder, and social anxiety disorder), but has also been proposed to be part of helpful processes (such as problem solving and post-traumatic growth). To account for these contradictory outcomes, it has been proposed that repetitive thought can be broken down into maladaptive abstract thought and relatively adaptive concrete thought (Watkins, 2008). However, there are currently no measures in the existing literature that assess these subtypes of repetitive thought. This thesis describes the development and validation of a transdiagnostic measure of abstract and concrete repetitive thought: the Repetitive Thought Scale (RTS). Studies 1a-4 describe the psychometric properties of a trait version of the RTS in three online samples and one university sample, whereas Studies 1b-4 describe the psychometric properties of a state version of the scale. Both versions of the scale demonstrated good factor structure, excellent reliability, and good predictive validity with symptoms of psychopathology. Interestingly, and contrary to hypothesis, concrete repetitive thought was found to be more strongly related to symptoms of psychopathology than abstract thought in these non-clinical samples. Study 5 demonstrated that the abstract subscale of the state version could be used as a manipulation check for experiments that involve repetitive thought inductions. Study 6 explored a longitudinal mediation model predicting psychopathology symptoms at the six-month follow-up using baseline symptoms as predictors. Only metacognitive beliefs about repetitive thought emerged as mediating variables in this model. Study 7 revealed that only abstract thought distinguished between never, previously and currently depressed individuals in a community clinical sample. Studies 8 and 9 compared the efficacy of rumination cues action and concrete thinking as strategies for reducing the frequency of repetitive thought. However, neither strategy emerged as efficacious in these experimental studies. Overall, these studies highlight the development of the repetitive thought scale, which is a reliable and valid transdiagnostic measure of abstract and concrete repetitive thought.