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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 factors are factors that influence outcome outside of the treatment context (Lambert 2003, Hubble et al. 2005). This thesis focuses on three extratherapeutic factors linked to social support from friends and family: perceived social support, number of social contacts and number of social confidantes. Previous research has shown that more frequent use of the DBT skills is associated with improved outcomes during DBT (Miller et al. 2000, Neacsiu et al. 2010, Stepp et al. 2008). This could suggest that skill use is a specific change mechanism in DBT. Alternatively, Wampold (2001) suggests that specific factors are associated with therapy outcome only because they enhance common factors. For instance, patients who use the skills more are likely to find their treatment more credible, to have a stronger alliance with their therapist, and to feel a stronger sense of self-efficacy. They may also receive more social support from friends and family. No research to date has examined whether skill use is associated with outcome independently of common and extratherapeutic factors. Such research could yield valuable information on how patients receiving DBT achieve change, and on what factors therapists and researchers should focus when aiming to improve outcomes. The first aim of this thesis is therefore to establish whether skills use is associated with the outcome of DBT for BPD independently of common and extratherapeutic factors. Secondly, patients with BPD are often considered to drop out of treatment more frequently than patients with other mental disorders (Bornovalova & Daughters 2004, 18 Horner & Diamond 1996, Kelly et al. 1992). However, very few studies have examined what processes occurring during treatment are associated with dropout. Previous research has shown that a stronger therapeutic alliance is associated with treatment completion in psychotherapy for BPD (Gunderson et al. 1997, Spinhoven et al. 2007, Yeomans et al. 1994). However, the predictive relevance of specific factors such as DBT skills use, other common factors such as treatment credibility or self-efficacy, and extratherapeutic factors such as social support, has not been evaluated. Furthermore, no study to date has examined whether the DBT skills are associated with treatment completion independently of common and extratherapeutic factors. Such research could enable a better understanding of why patients drop out of DBT treatment, and could inform what factors therapists should focus on to prevent this. The second aim of this thesis is therefore to establish whether skills use predicts treatment completion in DBT for BPD independently of common and extratherapeutic factors. Thirdly, quantitative research on the association between treatment processes and outcomes is arguably limited, because although it can show what factors are associated with outcome, it cannot show how these factors lead to better outcomes. By contrast, qualitative interviews with patients can yield valuable insights on how their experiences in therapy enabled them to achieve change, and can enable identification of barriers to change (Hodgetts & Wright 2007). This in turn can inform future quantitative work by giving an indication of what mediating and moderating factors could be evaluated, and can ensure that researchers’ understanding of change mechanisms during therapy remains rooted in the lived experiences of patients rather than tied to abstract academic theories (Black 1994, Denzin & Lincoln 1994, 19 Greenhalgh & Taylor 1997, Miles & Huberman 1994). Since the main focus of the present thesis is on the DBT skills, the qualitative element focuses on participants’ experiences of learning, using and gaining benefit from the skills. The aims are to explore how patients use the skills and how they come to gain maximum benefit from them, what factors facilitate this and what factors act as barriers to this. Based on the above aims, the thesis addresses the following three research questions: 1) Are the DBT skills associated with outcome independently of common and extratherapeutic factors? Specifically: a) Are the DBT skills associated with self-harm frequency during treatment independently of common and extratherapeutic factors? b) Are the DBT skills associated with BPD symptom severity during treatment independently of common and extratherapeutic factors? 2) Do the DBT skills predict treatment completion independently of common and extratherapeutic factors? 3) How do patients experience learning, using and gaining benefit from the DBT skills? Specifically: a) How do patients use the DBT skills? b) How do patients come to gain maximum benefit from the DBT skills? c) What factors facilitate patients in gaining maximum benefit from the DBT skills? d) What factors act as barriers to gaining maximum benefit from the DBT skills? 20 Questions One and Two are addressed using quantitative methods, whilst Question Three is addressed using qualitative methods. The structure of the thesis is outlined below. Chapters One to Four are Literature Review chapters whilst Chapters Five to Seven present empirical data collected and analysed by the doctoral candidate, and Chapter Eight is a Discussion chapter. Chapter One summarises the nature and treatment of BPD, the DBT model, evidence for its effectiveness and the need for research on its mechanisms. Chapter Two reviews the literature on specific, common and extratherapeutic factors in psychotherapy, describes the contextual model and reviews the evidence for and against it, and reviews evidence on the role of specific, common and extratherapeutic factors in DBT. Chapter Three systematically reviews the literature on predictors of symptom change in psychotherapy for BPD, in order to evaluate the weight of evidence in the field and to identify what potential predictors of outcome should be included in the predictive models evaluated in Chapter Five. |
