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There is a need to regularly update the evidence base on the effectiveness of online mindfulness-based interventions (MBIs), especially considering how fast this field is growing and developing.
This study presents an updated meta-analysis of randomized controlled trials assessing the effects of online MBIs on mental health and the potential moderators of these effects.
We conducted a systematic literature search in PsycINFO, PubMed, and Web of Science up to December 4, 2020, and included 97 trials, totaling 125 comparisons. Pre-to-post and pre-to-follow-up between-group effect sizes (Hedges
The findings revealed statistically significant moderate pre-to-post effects on depression (
Our findings not only demonstrate that online MBIs are booming but also corroborate previous findings that online MBIs are beneficial for improving mental health outcomes in a broad range of populations. To advance the field of online MBIs, future trials should pay specific attention to methodological quality, adherence, and long-term follow-up measurements.
In the 1970s, mindfulness was introduced as an intervention to tackle various psychological symptoms, such as stress, depression, and anxiety [
One year later, another meta-analysis focused on the same topic [
In 2018, Sevilla-Llewellyn-Jones et al [
In 2020, two more meta-analyses of technology-enabled and online MBIs were performed, focusing on stress management in the general population (n=16) [
Indeed, reviewing the literature from the past few years indicates that developments in the area of online mindfulness emphasize the need to regularly update the current evidence base. First, as anticipated, the field of online mindfulness is booming, as evidenced by dozens of studies that have been published since our previous meta-analysis. Incorporating these studies in a new meta-analysis would provide a more thorough assessment of the clinical and nonclinical utility of online MBIs and improve the power of moderation analyses. Second, we noticed a transformation in the types of online MBIs that are being delivered to users. At the time that our 2016 meta-analysis was conducted, MBSR and MBCT and derivatives from these interventions dominated the field. Since then, there has been a rapid increase in online ACT interventions, allowing a more robust assessment of this specific MBI. Third, it appears that the components of MBIs are increasingly mixed or hybrid, resulting in numerous MBIs that show considerable overlap and all seem to have a beneficial impact on mental health. It remains unclear whether mixtures of MBIs are equally effective in improving mental health. Fourth, not only is the content of today’s online MBIs different from 5 years ago but also the delivery method is different. MBIs are increasingly delivered through smartphone apps instead of websites, increasing access modality and ease of usage. These developments spurred the desire to update and extend our 2016 meta-analysis to provide more robust evidence of the short-term and long-term effects of online MBIs, as well as the potential moderators of these effects.
This study was conducted according to the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines [
We searched the PsycINFO, PubMed, and Web of Science databases three times for RCTs published since 2015—that is, September 6, 2018; July 19, 2019 (by MSS and WP); and December 4, 2020 (by JA). The search strategy was identical to that used in our previous meta-analysis [
Trials were included when they met the following criteria:
Examines the effectiveness of an MBI, that is, an intervention consisting of at least one guided or unguided session and a combination of psycho-education and more than one experiential exercise with a primary focus on enhancing mindfulness skills. Both mindfulness-only interventions (eg, MBSR and MBCT) and mindfulness-integrative interventions such as Dialectical Behavior Therapy, ACT, or Mindfulness-Based Compassionate Living were included. Derivatives and mixtures of programs were also eligible, provided that teaching mindfulness was at the core of the intervention.
The MBI is delivered via the internet and can be followed on a computer or a mobile device such as a smartphone or tablet. Interventions that used a combination of face-to-face and online sessions were eligible when face-to-face sessions were limited to the introduction of the study.
Use of a randomized controlled design with at least one experimental condition and one active or inactive control condition (ie, no treatment, usual care, or any active treatment other than the experimental intervention).
Depressive symptoms, anxiety symptoms, stress, well-being, or mindfulness was measured pre- and postintervention, using a validated measure.
Studies simultaneously using MBIs and non-MBIs were eligible for inclusion, provided that the design allowed us to distinguish the independent effects of the MBIs.
The study population consisted of adults aged ≥18 years. Both clinical (mental and physical disorders) and nonclinical samples (eg, students and community samples) were eligible.
The reported findings allow the calculation of effect sizes, or the necessary data were made available by the authors. In addition, RCT protocols were screened for eligibility and included when the authors provided the necessary data.
The selection of studies took place in three phases: first, the review of titles; second, abstracts; and third, full texts. The selection was conducted independently by MSS, JA, and WP. Disagreements were resolved through discussion.
Population, intervention, and methodological characteristics (
Three raters (alternatingly, MSS, JA, and WP) independently assessed the methodological quality of each study using the same criteria as outlined in [
Meta-analytic procedures were performed using the Comprehensive Meta-Analysis software, version 2.2.064. Hedges
Per outcome, forest plots of the pre-to-post effect sizes and pre-to-follow-up effect sizes were generated. A random effects model was used [
The statistical procedures used to assess heterogeneity, publication bias, and moderators were identical to those used in our previous meta-analysis [
The first search yielded 1328 hits, the second yielded 532 hits, and the last yielded 1014 hits. A total of 928 duplicates were removed. After reviewing 1946 titles, 678 abstracts, and 207 full articles, we identified 82 new studies, totaling 105 comparisons, which were not included in our previous meta-analysis (
Flowchart of the study selection process. MBI: mindfulness-based intervention; RCT: randomized controlled trial.
Although research on the effectiveness of online MBIs has been undertaken in 21 countries across the globe, nearly one-third of all studies were conducted in the United States (n=31). Other countries in the top 5 included the United Kingdom, Sweden, the Netherlands, and China with 12, 10, 8, and 5 RCTs, respectively.
The total study population consisted of 17,464 participants, with a mean age of 40 years. A total of 9066 participants were in the experimental condition and 7832 were in the control condition. There were large differences in sample sizes, ranging from 16 in a small-scale pilot RCT [
In 70.4% (88/125) of comparisons, a mindfulness-only intervention was used, with the most commonly studied intervention being MBSR (n=21), followed by MBCT (n=14), and a mixture or derivative of MBSR and MBCT and related exercises (n
MBIs were mostly delivered through a website (n=84), followed by an app (n=27), virtual online classroom or videoconferencing software (n=4), or a combination (n=3). The number of online MBI sessions varied between 2 and 45. Sessions were used over a period of 10 days to 14 weeks. In 28.8% (36/125) of comparisons, online MBIs were provided with therapist guidance.
In 52% (65/125) of comparisons, the effectiveness of online MBIs was examined relative to a waitlist control (n=61) or no intervention (n=4) condition. An active control condition was used in 48% (60/125) of comparisons, including psycho-education (n=13), an online discussion forum (n=7), treatment as usual (n=14), and an alternative intervention (n=26; eg, expressive writing, cognitive behavioral therapy, and behavioral activation).
Outcome measures for depressive symptoms, anxiety, stress, well-being, and mindfulness were administered in 82, 70, 54, 48, and 67 comparisons, respectively; 44.3% (43/97) of studies reported not only pre- and postmeasurement but also follow-up measurements, with follow-up times ranging from 1 to 12 months.
Although 70% (68/97) of studies reported important information regarding adherence to the intervention (eg, time spent on the intervention, number of modules started, number of completed sessions, and daily meditation practice), only 23% (22/97) studies provided a definition or cut-off to determine adherence versus nonadherence. Using various definitions of adherence, these studies reported adherence rates ranging from 35% to 92%.
Scores for methodological quality varied between 1 and 7 points (
Results of methodological quality assessment per criterion presented as percentages across all included studies.
Pre-to-post effects of online mindfulness-based interventions compared with controlsa.
Outcomes |
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Hedges |
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Heterogeneity | Fail-safe |
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Depression | 89 | 0.34 (0.18 to 0.50) | 4.10c | 1326.41c | 93.37 | 5507 |
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Anxiety | 74 | 0.26 (0.18 to 0.33) | 6.70c | 208.10c | 64.92 | 2763 |
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Stress | 56 | 0.44 (0.32 to 0.55) | 7.48c | 262.80c | 79.07 | 1355 |
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Well-being | 52 | 0.21 (–0.03 to 0.45) | 1.75 | 1516.62c | 96.64 | 121 |
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Mindfulness | 72 | 0.40 (0.30 to 0.50) | 7.72c | 407.80c | 82.59 | 2624 |
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Depressiond | 86 | 0.30 (0.14 to 0.46) | 3.69c | 1254.96c | 93.23 | 2903 |
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Anxietye | 67 | 0.22 (0.15 to 0.28) | 6.62c | 112.35c | 41.26 | 1217 |
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Stressf | 47 | 0.38 (0.29 to 0.48) | 7.72c | 130.94c | 64.87 | 1947 |
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Well-beingg | 46 | 0.22 (0.15 to 0.29) | 6.02c | 89.18c | 49.54 | 727 |
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Mindfulnessh | 65 | 0.39 (0.29 to 0.49) | 7.65c | 180.91c | 74.37 | 3719 |
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Depression | 61 | 0.37 (0.27 to 0.47) | 7.43c | 237.26c | 74.71 | 2196 |
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Anxiety | 55 | 0.28 (0.20 to 0.37) | 6.35c | 157.54c | 65.72 | 1563 |
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Stress | 38 | 0.39 (0.27 to 0.51) | 6.26c | 159.77c | 76.84 | 1433 |
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Well-being | 31 | 0.26 (0.12 to 0.41) | 3.50c | 154.25c | 80.55 | 398 |
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Mindfulness | 45 | 0.43 (0.29 to 0.56) | 6.20c | 259.72c | 83.06 | 2486 |
aAnalyses were conducted using a random effects model.
b
c
dThree outliers were removed: Kladnitski et al [
eSeven outliers were removed: Forbes et al [
fNine outliers were removed: Allexandre et al [
gSix outliers were removed: Allexandre et al [
hSeven outliers were removed: Forbes et al [
Whereas visual inspection of funnel plots indicated no remarkable evidence of publication bias, trim-and-fill analyses and fail-safe numbers suggest that publication bias has occurred in the reporting of effects on depressive and anxiety symptoms, well-being, and mindfulness. The Duval and Tweedie [
Subgroup analyses can be found in
The meta-regression analysis (
Meta-regression analysesa.
Outcome and predictor |
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Slope |
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Study quality | 88 | 0.05 | 1.09 | .28 | ||||
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84 | 0 | 0 | .99 | |||||
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Mean age | 80 | 0 | 0.47 | .64 | ||||
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% female | 87 | 0.01 | 1.37 | .18 | ||||
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Study quality | 73 | 0.07 | 2.04 | .04c | ||||
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69 | 0 | –1.25 | .21 | |||||
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Mean age | 66 | 0 | –0.03 | .98 | ||||
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% female | 73 | 0 | 0.83 | .40 | ||||
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Study quality | 55 | –0.04 | –0.74 | .46 | ||||
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49 | 0.03 | 2.45 | .05 | |||||
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Mean age | 43 | 0.01 | 2.88 | .004d | ||||
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% female | 55 | 0 | 0.25 | .80 | ||||
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Study quality | 51 | 0.07 | 0.90 | .37 | ||||
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49 | 0 | –0.33 | .74 | |||||
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Mean age | 51 | 0 | –0.28 | .78 | ||||
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% female | 51 | 0 | 0.17 | .86 | ||||
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Study quality | 71 | 0.01 | 0.26 | .80 | ||||
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66 | –0.01 | –2.80 | .005d | |||||
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Mean age | 65 | 0 | 0.06 | .95 | ||||
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% female | 71 | 0.01 | 1.83 | .07 |
aMeta-regression analyses were conducted using a mixed effects model with unrestricted maximum likelihood.
b
c
d
The pre-to-follow-up effects are shown in
Pre-to-follow-up effects of online mindfulness-based interventions compared with controlsa.
Outcomes |
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Hedges |
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Heterogeneity | Fail-safe |
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Depression | 26 | 0.25 (0.12 to 0.38) | 3.80c | 74.12c | 66.27 | 201 | |
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Anxiety | 21 | 0.23 (0.13 to 0.32) | 4.62c | 31.49d | 36.49 | 189 | |
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Stress | 15 | –0.24 (–0.40 to –0.08) | –2.97e | 37.09e | 62.25 | 71 | |
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Well-being | 18 | –0.02 (–0.53 to 0.49) | –0.09 | 1254.86c | 98.73 | 171 | |
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Mindfulness | 27 | 0.06 (–0.05 to 0.16) | 1.09 | 75.05c | 65.36 | 0 | |
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Depressionf | 25 | 0.27 (0.14 to 0.40) | 4.18c | 53.93c | 55.50 | 220 | |
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Anxiety | N/Ag | N/A | N/A | N/A | N/A | N/A | |
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Stressh | 13 | –0.11 (–0.21 to –0.02) | –2.31d | 9.35 | 0 | 12 | |
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Well-being | N/A | N/A | N/A | N/A | N/A | N/A | |
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Mindfulnessi | 25 | 0.05 (–0.03 to 0.14) | 1.23 | 40.36d | 40.53 | 0 | |
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Depression | 16 | 0.24 (0.09 to 0.38) | 3.23e | 32.06e | 53.21 | 75 | |
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Anxiety | 13 | 0.21 (0.07 to 0.34) | 2.99e | 21.26d | 43.56 | 45 | |
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Stress | 11 | –0.30 (–0.51 to –0.08) | –2.67e | 34.51c | 71.02 | 44 | |
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Well-being | 13 | 0.17 (–0.03 to 0.37) | 1.71 | 48.02c | 75.00 | 24 | |
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Mindfulness | 18 | 0.08 (–0.08 to 0.23) | 0.96 | 56.78c | 70.06 | 0 |
aOnly studies with a follow-up period of 1-3 months were included. Analyses were conducted using a random effects model.
b
c
d
e
fOne outlier was removed: Mak et al [
gN/A: not applicable.
hTwo outliers were removed: Kladnitski et al [
iTwo outliers were removed: Pots et al [
For depression, anxiety, and well-being, funnel plots were somewhat skewed in favor of studies with a positive outcome at follow-up. The trim-and-fill procedure by Duval and Tweedie indicated publication bias for all outcomes except stress; 1, 3, 6, and 6 studies were trimmed for depression, anxiety, well-being, and mindfulness, respectively. The adjusted effect sizes for depression (
An updated meta-analysis was conducted to assess the effects of the booming field of online MBIs on mental health across studies. In total, 97 RCTs were included in this meta-analysis, demonstrating the rapidly growing interest in implementing MBIs via eHealth platforms and apps. In comparison, only 15 RCTs were included in our meta-analysis conducted 5 years ago [
Thus, when addressing depression and anxiety, the impact of online MBIs appears similar to MBIs in traditional face-to-face format [
Our findings on well-being deserve special attention. In our updated meta-analysis, a significantly small effect on well-being was found, but only after omitting outliers (
The finding that studies of moderate-to-high quality indicate a positive impact of online MBIs on well-being is important because interventions such as MBSR, MBCT, and ACT emphasize well-being as an intervention outcome. Its relevance is further underlined by increasing evidence that mental well-being and mental illness are related yet discernible phenomena [
Remarkably, where online MBSR and online MBCT were the most prominent online MBIs 5 years ago, in this meta-analysis, online ACT dominates the field; 29 studies evaluated the impact of online ACT interventions compared with 5 studies in 2016 [
Whereas online ACT may have become an increasingly common type of intervention in this field of study, another development that is mirrored by our findings is that interventions are increasingly nonspecific. In 42.5% (53/125) of the comparisons, mixed or hybrid interventions, encompassing elements of both MBSR and MBCT as well as other mindfulness-based exercises, were used. We found that these programs prove to be effective in reducing symptoms of depression (
Subgroup analyses yielded significant differential effects of guidance, symptoms, and type of control group on stress, anxiety, and mindfulness. The effects of online MBIs on stress were significantly higher for interventions with therapist guidance (
Although the field of online mindfulness is booming, we noticed a number of undesirable phenomena that may undermine the accumulation of unbiased scientific knowledge in this specific domain, thereby hampering the development and optimization of novel online MBIs. The first phenomenon was related to adherence. Adherence is an important topic in the context of online interventions [
The indications for publication bias that were found for all outcomes except stress represent a second phenomenon. The pre-post effect size for well-being was substantially reduced after adjusting for missing studies, whereas pre-post findings for depression and anxiety indicated the opposite. We encourage researchers and publishers to publish not only studies with positive outcomes but also studies with nonsignificant or negative findings to overcome the accumulation of unbiased scientific knowledge and the unduly hampering optimization of novel online MBIs.
A third phenomenon that should be addressed is an increase in the proportion of studies with a high risk of bias from 20% (3/15 studies) in our previous meta-analysis [
This meta-analysis included a large number of studies, which allowed moderator analyses and long-term follow-up measurements. However, some important limitations of this study must be considered. There was great variability in follow-up measurements, and the studies included in this meta-analysis only allowed for an overall assessment of effects until the 3-month follow-up. Owing to the limited number of studies using longer follow-up times (longer than 3 months), it remains unclear whether the effects of online MBIs remain at long-term follow-up. It should also be noted that heterogeneity was high for most moderator analyses. This suggests that other, yet unknown, factors may explain the effect differences rather than the observed factors.
This updated meta-analysis not only demonstrates that the field of online MBIs is booming, with a significant low-to-moderate impact on mental health, but also corroborates previous evidence that online MBIs are beneficial for a wide range of populations and symptoms. Future trials assessing the effectiveness of online MBIs should focus on methodological quality parameters, on a priori definition and monitoring of adherence, and on longer follow-up measurements.
Study characteristics and outcome measures.
Methodological quality of studies included in the meta-analysis.
Subgroup analyses.
Acceptance and Commitment Therapy
Mindfulness-Based Cognitive Therapy
mindfulness-based intervention
Mindfulness-Based Stress Reduction
Preferred Reporting Items for Systematic Reviews and Meta-Analyses
randomized controlled trial
MSS and WP designed the study. MSS and JA conducted the literature search. MSS, JA, and WP performed data extraction and analyses. EB was an advisor for the project. MSS prepared the first draft of the manuscript, and all authors contributed to and approved the final manuscript.
None declared.