The research presented in this thesis explored unguided self-help therapy, primarily using a gratitude technique. Psychological mechanisms that underlie the placebo response may also play a primary role in beneficial response to unguided selfhelp therapy. Retention (whether participants completed the intervention), outcome (whether the technique effectively reduced symptoms), and mechanisms (the psychological processes which antecede outcome and retention), were investigated with participants engaging in procedures to improve a diverse range of symptoms, namely, mood, sleep disturbance, body dissatisfaction, depression and anxiety. Studies one and two investigated the role of two placebo mechanisms, response expectancy and motivational concordance, as predictors of outcome following a gratitude technique. Response expectancy contributed to outcome to a greater extent in a laboratory setting, whereas motivational concordance explained greater outcome variance in a real-world setting. Studies three, four and five compared a gratitude technique to a problemfocused technique and a wait list control. Across all three studies, being randomly allocated to a gratitude technique resulted in greater retention than being a llocated to a problem-focused technique. Use of a gratitude technique resulted in equivalent significant reductions in body dissatisfaction (Study three), depression (Study four) and worry (Study five), compared to a problem-focused cognitive restructuring technique, and was significantly more effective than being on a waitlist in all three studies. There was some evidence that different mechanisms affect outcome and retention. Placebo theory and the contextual model of psychotherapy provide useful insight into the factors that affect outcome and retention in self-help therapy.

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