The overall goals of the studies included in this dissertation were a) to investigate the effectiveness of MBCT for chronic, treatment resistant depression, b) to explore cognitive reactivity and rumination as potential working mechanisms of MBCT and c) to investigate the psychometric properties of the Dutch translation of a novel, comprehensive questionnaire to assess mindfulness skills. This chapter summarizes and discusses the studies in relation to the existing literature. In addition, strengths and limitations are identified and directions for future research and clinical implications are given.
Chapter 2 describes the rationale, design and methods of the RCT comparing MBCT with treatment-as-usual (TAU) for chronically, treatment-resistant depressed patients. All participants were depressed for at least 12 months, despite of at least 10 sessions of evidence-based psychological treatment, such as CBT or IPT and treatment with at least one antidepressant (> 4 weeks) during the current episode. At the beginning of the study all participants were moderately to severely depressed. Before and after the MBCT or treatment-as-usual (TAU), depressive symptoms, rumination, quality of life, mindfulness skills and self-compassion were assessed. In addition, remission rates were investigated with a psychiatric interview according to DSM-IV criteria.
Chapter 3 presents the findings of this RCT. In total, 106 participants were included in the study. Results of the intention-to-treat analyses including all available data show that there was no significant difference in reduction of depressive symptoms between the conditions. However, at post-treatment more participants of the MBCT condition compared with TAU reached (partial) remission from their depressive disorder. In addition, participants of the MBCT group showed significant less rumination, a higher quality of life, more mindfulness skills, and more self-compassion compared with TAU. The percentage of participants who dropped out of the MBCT was higher than expected, i.e. 24.5%. When only including completers of the MBCT in the analysis (‘per-protocol analysis’), the MBCT condition did show a significant reduction in depressive symptoms compared with TAU. Severity of symptoms, treatment-resistancy and childhood trauma did not moderate the effect of MBCT or TAU on depressive symptoms. However, baseline levels of rumination did moderate the effect of MBCT on depressive symptoms. Participants with high levels of rumination on baseline showed significantly lower depressive symptoms post-treatment when allocated to MBCT compared with TAU. This implies that chronically, treatment-resistant depressed patients who experienced high levels of rumination seemed to benefit most of MBCT.
Chapter 4 and 5 both investigated dysfunctional cognitive processes as potential working mechanisms of MBCT. In data of another RCT in remitted depressed patients (N=115) were analyzed to test whether MBCT compared with a waitlist-group affects cognitive reactivity. As previous analyses showed that MBCT reduces depressive symptoms in this sample, we also investigated whether cognitive reactivity mediated the effect of MBCT on depressive symptoms. Results showed that after MBCT, cognitive reactivity was indeed significantly diminished in the MBCT group and that cognitive reactivity mediated the effect of MBCT on depressive symptoms. This provides preliminary evidence for cognitive reactivity as a potential working mechanism of MBCT. Chapter 5 investigated the effects of MBCT on rumination in a sub-sample (n=62) of the RCT described in chapter 2 and 3. Rumination is typically assessed with self-report questionnaires. Although easy to administer, questionnaires might be influenced by memory and response bias. In chapter 5, we therefore utilized a new, on-line behavioral measure of rumination, called the ‘breathing focus task’ (BFT). Because the BFT has never been used in a clinically depressed sample, we first compared the chronically, treatment-resistant depressed sample (n=62) with a never-depressed sample (n=106) matched on age and gender. Results show that chronically, treatment-resistant depressed patients have significantly more negative -but not more neutral or positive- thought intrusions on the BFT compared with the never-depressed controls. Higher levels of negative thought intrusions were associated with a self-report measure of rumination and patients showed an increase in sad mood. Secondly, the scores on the BFT of the chronically, treatment-resistant depressed sample were compared before and after MBCT and TAU. As expected, the MBCT group showed a significantly larger decrease in negative thought intrusions after treatment than the TAU group. This study supports the hypothesis that MBCT reduces state rumination.
In chapter 6, the validity of the Dutch translation of a new questionnaire to assess mindfulness skills is presented. Recent studies have questioned whether the factor structure of one of the most frequently used questionnaires to assess mindfulness skills (FFMQ) is independent of meditation experience. Bergomi et al. (2014) developed a new questionnaire (Comprehensive Inventory of Mindfulness Experiences; CHIME) based on all available mindfulness questionnaires and reformulated items to make sure that the understanding of items is independent of mindfulness experiences. However, the CHIME was not yet available in Dutch. We translated the CHIME to Dutch and tested its factor structure, internal consistency, and its discriminant and convergent validity in a sample (N=481) consisting of clinical and non-clinical subsamples. Furthermore, a short version of the CHIME (CHIME-SF) was developed and the CHIME and CHIMESF were administered before and after MBCT or MBSR training. Results show that the psychometric properties of the CHIME were acceptable and that the CHIME and CHIMESF were both sensitive to change.
Please click HERE to access the thesis