| Summary: | PhD This thesis investigates the role of specific, common and extratherapeutic factors in dialectical behaviour therapy (DBT) for borderline personality disorder (BPD) with self-harm, using both quantitative and qualitative methods. The overall aim is to generate evidence on the mechanisms by which patients with BPD can achieve change. The premise of the thesis is that DBT has been shown to be more effective than control treatments in reducing self-harm in patients with BPD (Brazier et al. 2007, Binks et al. 2006, Stöffers et al. 2012), but the mechanisms by which this is achieved have not been empirically established. Identification of these mechanisms could enable them to be enhanced in existing interventions or even in routine treatment for patients with BPD, so that improved outcomes are achieved (Llewellyn & Hardy 2001, Kazdin 2007). Theories on the mechanisms of change in psychotherapy have identified three types of factor that may contribute to treatment outcome: specific factors, common factors and extratherapeutic factors. Specific factors are those outlined in the theory of a particular therapy as a central mechanism for patient change (Oei & Shuttlewood 1996). In DBT, patients are taught a set of skills to better regulate their emotions, and patients’ use of these skills is identified in the DBT manual as a key mechanism for achieving change (Linehan 1993a, b). Linked to this, the thesis focuses on three specific factors in DBT: perceived understanding, frequency of use and perceived helpfulness of the DBT skills. Common factors are aspects of treatment which are common to all therapies (Oei & Shuttlewood 1996). The contextual theory outlines several factors common to all successful psychotherapy interventions, and argues that these common 17 factors are the key agents of change (Frank & Frank 1991, Wampold 2001). This thesis focuses on three common factors identified by the contextual theory: treatment credibility, the therapeutic alliance, and self-efficacy. Extratherapeutic ...
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