Mindfulness-based therapy: A comprehensive meta-analysis
Introduction
An increasing number of meta-analyses and systematic reviews have investigated the effectiveness of mindfulness-based therapy (MBT). These reviews reported inconsistent findings about the size of the treatment effect of MBT for reducing stress, anxiety, and depression associated with physical illness or psychological disorders (Baer, 2003, Bohlmeijer et al., 2010, Chiesa and Serretti, 2010, Chiesa and Serretti, 2011, Cramer et al., 2012, de Vibe et al., 2012, Eberth and Sedlmeier, 2012, Fjorback et al., 2011, Grossman et al., 2004, Hofmann et al., 2010, Klainin-Yobas et al., 2012, Ledesma and Kumano, 2009, Musial et al., 2011, Piet and Hougaard, 2011, Sedlmeier et al., 2012, Zainal et al., 2012).
These inconsistencies may be due to a number of factors, including the choice of the MBT protocols, the restriction to specific research designs, and the inclusion of a particular group of patients. Moreover, little is known about the stability of treatment gains (Baer, 2003, Hofmann et al., 2010), about the active ingredients that may account for the efficacy of MBT (Chiesa and Serretti, 2011, Fjorback et al., 2011), and about the relevant moderator variables. It is assumed that mindfulness is a central mechanism of MBT (e.g., Bränström et al., 2010, Greeson et al., 2011, Kuyken et al., 2010, Shahar et al., 2010) that might enhance positive affect, decrease negative affect, and reduce maladaptive automatic emotional responses (Gross, 2007, Hofmann et al., 2012, Koole, 2009, Thompson, 1991, Thompson, 1994). Although this is consistent with the notion that mindfulness training is associated with changes in areas of the brain responsible for affect regulation, and stress impulse reaction (Davidson et al., 2003, Hölzel et al., 2011, Lazar et al., 2005) the empirical evidence for explaining the mechanisms of MBT remains sparse. Similarly, little is known about the potential moderators, including treatment duration (de Vibe et al., 2012, Hofmann et al., 2010, Klainin-Yobas et al., 2012, Sedlmeier et al., 2012), homework practice (e.g., Carmody and Baer, 2009, Fjorback et al., 2011, Toneatto and Nguyen, 2007), course attendance (de Vibe et al., 2012), and the clinical and mindfulness training and practical experience of the therapists delivering MBT (Carmody and Baer, 2009, Crane et al., 2010, Davidson, 2010, Fjorback et al., 2011, Piron, 2001, Pradhan et al., 2007, Segal et al., 2002).
In order to address the weaknesses of the current literature, we conducted a comprehensive effect-size analysis with the following objectives: (1) to quantify the size of the treatment effect with the maximum available data; (2) to investigate and quantify the role of mindfulness in MBT; and (3) to explore moderator variables.
Section snippets
Eligibility criteria
Any study examining the pre-post or controlled effects of MBT for a wide range of physical and medical conditions, psychological disorders, and in non-clinical populations was considered in our analysis. Studies were excluded if they (1) did not include a mindfulness meditation-based intervention; (2) did not aim to examine treatment effects; (3) consisted of comparisons among meditators or among meditation styles; (4) examined the non-direct effects of mindfulness (i.e., mindfulness treatment
Study selection
PubMed searches produced 902 publications and PsycINFO searches yielded 1974 publications (including 278 dissertations). We carefully assessed the identified publications and applied the exclusion criteria, resulting in 209 studies (177 from journal articles and 32 from dissertations). Of the 209 studies, 207 reported post-treatment assessments, and two of them reported only follow-up data. The study selection process is illustrated in detail in Fig. 1.
Study characteristics
The effect size (Hedge's g) and other
Discussion
This meta-analysis examined 209 studies with a combined total of 12,145 participants of diverse ages, genders, and clinical profiles. The wide variety of studies, the variety of participants, and the use of meta-analytic validity measures allowed us to clarify some inconsistencies concerning the therapeutic value of MBT. The results showed that MBT is moderately effective in pre-post studies. When compared to some other active treatments (including psychoeducation, supportive therapy,
Funding
No official funding was provided to conduct the current meta-analysis. Materials (e.g., software) were provided by the Laboratory for Education on Schizophrenia and Psychoses Oriented to Intervention and Recovery of Dr. Tania Lecomte. Dr. Hofmann is funded in part by NIMH grant R01 MH081116.
Note. A complete list of references for publications included in the meta-analysis is available in Appendix B.
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