This review concluded that mindfulness-based therapy was moderately to largely effective for a variety of psychological problems, particularly for reducing anxiety, depression and stress.
Eligible was any study evaluating the before-and-after or controlled effects of mindfulness-based therapy for physical or medical conditions, for psychological disorders, or for a non-clinical population. Studies were excluded if they compared mediation styles or mediators, examined the non-direct effects of mindfulness, used mindfulness as a component of another treatment, or were based on meditation instruction, induction or retreats. Studies had to report sufficient information to calculate effect sizes for clinical (physical or psychological) or mindfulness outcomes.. Case studies were excluded.
In the included studies, a variety of mindfulness therapies were used, including mindfulness-based awareness processes, stress reduction, cognitive therapy, relapse prevention and yoga. Controlled studies used either a treatment or waiting list, as the control. The most common disorders were mood and cancer (some studies included caregivers), anxiety, pain, alcohol or substance abuse, fibromyalgia, overweight or obesity, social anxiety or social phobia, HIV, post-traumatic stress disorder, and headache. Many studies included more than one disorder. Outcomes were measured by a variety of instruments (details in the paper).
One reviewer selected studies for inclusion and decisions were checked by a second reviewer. Disagreements were resolved through discussion, or by contacting the original study's authors.
Results of the Review
There were 209 studies, with 12,145 participants; 109 were randomised controlled trials (RCTs), 26 were non-randomised controlled studies, 72 were uncontrolled before-and-after studies, and two only reported follow-up data. The controlled studies had a mean quality score of 4.84 (out of 11). The before-and-after studies had a mean quality score of 2.93 (out of 5). In studies with follow-up, it ranged from three weeks to three years. Attrition ranged from none to 81.5%.
For clinical outcomes, at the end of treatment, mindfulness-based therapy was significantly more effective than psychological education (Hedges' g 0.61, 95% CI 0.27 to 0.96; nine studies; I²=83%), supportive therapy (Hedges' g 0.37, 95% CI 0.17 to 0.57; seven studies; I²=64%), relaxation procedures (Hedges' g 0.19, 95% CI 0.03 to 0.35; eight studies; I²=59%), and imagery or suppression techniques (Hedges' g 0.26, 95% CI 0.10 to 0.53; two studies; I²=0).
There were no significant differences between mindfulness-based therapy and traditional cognitive-behavioural therapy or other behavioural therapy (nine studies), or pharmacological treatments (three studies).
Analysing before-and-after and waiting-list controlled studies separately, at the end of treatment the effect sizes for mindfulness-based therapy were larger for treatment for psychological disorders, than for physical or medical conditions.
There was a large, significant effect for anxiety in 10 before-and-after studies (Hedges' g 0.89, 95% CI 0.71 to 1.08; I²=14%), and four waiting-list controlled studies (Hedges' g 0.96, 95% CI 0.67 to 1.24). There was a moderate, significant effect for depression in five before-and-after studies (Hedges' g 0.69, 95% CI 0.52 to 0.86) and eight waiting-list controlled studies (Hedges' g 0.53, 95% CI 0.32 to 0.73). There was a moderate to high, significant effect for non-clinical populations in 18 before-and-after studies (Hedges' g 0.65, 95% CI 0.51 to 0.80) and 16 waiting-list controlled studies (Hedges' g 0.62, 95% CI 0.42 to 0.82). Statistical heterogeneity was reported to be high (details not given).
The results at follow-up were similar to those at the end of treatment (details reported).
For mindfulness outcomes, the effects of mindfulness-based therapy, at the end of treatment were lower in 23 treatment controlled trials (Hedges' g 0.42, 95% CI 0.27 to 0.57) than in 28 waiting-list controlled studies (Hedges' g 0.53, 95% CI 0.42 to 0.65) and 42 before-and-after studies (Hedges' g 0.69, 95% CI 0.59 to 0.80). Statistical heterogeneity was reported to be moderate (details not given). The effects were similar at follow-up. Other results were reported.
There was no evidence of publication bias. The clinical significance analyses corroborated the findings, showing that the severity of the initial anxiety and depression was reduced after treatment. The results of the meta-regression were reported.
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