There is a growing evidence-base for the efficacy of mindfulness courses—be that Mindfulness Based Stress Reduction (MBSR; Kabat Zinn 1982
) or Mindfulness Based Cognitive Therapy (MBCT; Segal et al. 2002
)—for a range of chronic health problems such as depression, chronic pain and anxiety disorders (Grossman et al. 2004
). Research has also shown that perceived stress decreases after taking part in a mindfulness intervention with benefits maintained at follow-up between 1 and 3 months (Carmody et al. 2009
; Krusche et al. 2012
). However, with the exception of two studies which assessed online interventions (Gluck and Maercker 2011
; Krusche et al. 2012
), previous studies considering the effect of mindfulness on perceived stress have assessed group-based face-to-face mindfulness interventions. As awareness of the benefits of mindfulness-based therapy increases, so does the need to improve access to these types of interventions. One way to increase access is to deliver interventions online. In addition to reducing the costs and decreasing waitlist times, operationalising interventions online enables participants to complete them from the comfort of their own home and in their own time. Furthermore, accessibility could be improved for a large number of people who may benefit but who may not be able to physically attend a face-to-face course (Finucane and Mercer 2006
However, there are challenges associated with proposing the delivery of mindfulness courses online. Traditionally, mindfulness interventions are conducted face-to-face (in groups) facilitated by mindfulness trainers. Developers of mindfulness-based interventions suggest that the presence of others is an important part of the learning process because, not only do other group members provide social support, they also learn from engaging in investigative dialogue (between the teacher and group members) at the end of each class (Kabat-Zinn 1990
; Segal et al. 2002
). Indeed, this position is supported by qualitative studies suggesting that participants find the group context largely very helpful (e.g. Allen et al. 2009
; Mason and Hargreaves 2001
While in theory online mindfulness interventions may be a cost-effective way forward, there is limited research assessing their efficacy. In a pilot study, Gluck and Maercker (2011
), employing a randomised waitlist control design, assessed the effect of a 2-week web-based mindfulness intervention on perceived stress, distress and mindfulness and reported that the intervention showed a non-significant trend of improvement for all measures (with medium effect sizes; d
= 0.46–0.77). Krusche et al. (2012
), in a pre-post study, assessed an online mindfulness course for its effect on perceived stress and reported a significant reduction with a large effect size (d
= 1.57) which was stable at 1-month follow-up. The lack of a control group does raise the question as to whether or not this was a general treatment effect; however, the effect size was of similar magnitude to other studies assessing face-to-face mindfulness interventions for stress. For example, Shapiro et al. (2007
), employing a randomised waitlist control design, assessed the impact of an MBSR intervention, found a medium between-groups effect size (d
= − 0.70), and in another randomised waitlist control trial, the authors reported a large between-group effect size for an MBSR intervention (d
= 0.91, Nyklicek and Kuijpers 2008
). Furthermore, a recent meta-analysis focussing exclusively on studies assessing online mindfulness-based interventions (n
= 15; predominantly MBSR), reported small but beneficial effects on depression (g
= 0.29), and anxiety (g
= 0.22), and moderate effects for the reduction of stress (g
= 0.51; Spijkerman et al. 2016
Understanding how mindfulness works will help us to identify those for whom it will be most effective. However, few studies are designed to understand “why” and/or “how” mindfulness delivers its benefits (Glomb et al. 2011
); therefore, intervention studies need to be constructed in order to assess possible mechanisms of change. Shapiro et al. (2006
) suggest two approaches. Firstly, dismantle (tease apart) studies can separate out and compare various active ingredients in mindfulness-based interventions, and secondly, studies can examine the central construct of mindfulness to establish whether the development of “mindfulness” (or different facets of mindfulness) leads to the positive changes that have been observed. This step can be facilitated by employing valid and reliable measures of mindfulness for use in statistical models of mediation.
Rounsaville and Carroll’s (2001
) three-stage model of behavioural therapies research articulates progressive stages of development and evaluation of behavioural treatments. Stage one focusses on the development of the intervention and conducting feasibility and pilot trials; Stage two focusses on conducting initial efficacy trials to evaluate manualised and pilot-tested treatments which have shown promise; and Stage three focusses on conducting larger RCTS with well-chosen control groups to establish generalisability, implementation challenges and cost-effectiveness. Similarly, in the National Institutes Health Stage Model (Onken et al. 2014
), a six-stage progressive model is proposed in the development of behavioural therapies. The current study is situated in stage 2 according to Rounsaville and Carroll, and to the equivalent stage (stage three) in the National Institutes Health Stage Model. We predicted that, in comparison to participants in the waitlist control group, participants who completed the mindfulness course would report significantly lower levels of perceived stress (H1), depression (H2) and anxiety (H3), immediately after course completion. We also sought to explore whether any treatment gains were maintained at 3 and 6-month follow-up (H4).
Intervention Effects on Outcome Variables
In the MANCOVA analysis, T2 scores (end of course for the INT group, end of waitlist period for the WLC group) for perceived stress, depression and anxiety were entered as the dependent variables; T1 scores (baseline) were entered as covariates and group (INT, WLC) was entered as the predictor. Analysis showed a significant multivariate main effect for group, Wilks’ λ = 0.57, F
(3, 111) = 28.34, p
< 0.001, ƞp2
= 0.43. ANCOVA analyses showed a significant reduction in perceived stress, F
(1, 115) = 63.32, p
< 0.001, d
= − 1.25 (95% CI [− 1.64, − 0.85]); depression, F
(1, 115) = 56.37, p
< 0.001, d
= −1.06 (95% CI [− 1.44, − 0.67]) and anxiety, F
(1, 115) = 67.86, p
< 0.001, d
= −1.09 (95% CI [− 1.47, − 0.98]). Table 3
shows that the between-group effect sizes for all outcomes after course completion were large (Cohen 1988
Means, standard deviations (SDs) and between group effect sizes for Outcome Variables for Intervention and Waitlist Control Groups: Intention-to-Treat and Per-Protocol Analysis
Intention to treat
Before treatment (T1)
After treatment (T2)a
Effect size d [95% CI]b
− 1.25 [− 1.64, − 0.85]
− 1.06 [− 1.44, − 0.67]
− 1.09 [− 1.47, − 0.98]
Before treatment (T1)
After treatment (T2)a
Effect size d [95% CI]b
− 1.20 [− 1.61, − 0.77]
− 0.98 [− 1.38, − 0.56]
− 1.01 [− 1.42, − 0.59]
Manipulation Check: Mindfulness Facets
In the MANCOVA analysis, T2 scores for describing, acting with awareness, non-judging and non-reacting were entered as the dependent variables; T1 scores were entered as covariates and group (INT, WLC) was entered as the predictor. Results showed a significant main effect for group, Wilks’ λ = 0.77, F[4, 109] = 7.97, p < 0.001, ƞp2 = 0.23. ANCOVA analyses showed that the intervention significantly increased levels of AA, F(1, 115) = 42.94, p < 0.001, ƞp2 = 0.27; DES, F(1, 115) = 5.76, p = 0.02, ƞp2 = 0.05 (ITT) [F(1, 100) = 2.47, p = 0.12 (PP)] and NJ, F(1, 115) = 26.13, p < 0.001, ƞp2 = 0.19. However, the intervention did not affect NR, F(1, 115) = 1.71, p = 0.19.
Separate multiple parallel mediation models were tested (see Table 4
) whereby change scores for describing, acting with awareness and non-judging were entered simultaneously to assess whether they mediated the effect on the intervention on each of our outcome variables. For each outcome, in PROCESS, using model 4 (for multiple mediators): respective T2 scores were entered as the dependent variable (Y); Group (INT, WLC) was entered as the Independent variable (X) and describing, acting with awareness and non-judging were entered as mediators (M). In the top half of Table 4
, a graphical representation of the mediation models for ITT and PP analysis are shown. The unstandardised Betas and standard errors (in brackets) for the effect of the intervention (intervention vs. waitlist control) on the mediators are embedded within this graphic on the relevant pathways. The bottom half of the table shows the effect of the mediators on each of the outcome variables. These figures correspond to the pathways in the graphic above from the mediators to the outcomes, with the A pathway being related to Describing, the B pathway being related to Acting with awareness and the C pathway relating to Non-judging. In order for a mediator to be significant, both pathways from the Intervention to the mediator from the mediator to the outcome must be significant.
Intention-to-Treat and Per-Protocol Unstandardised Betas (Standard Errors) and explained variance (R2) for the indirect effects of the intervention on the outcomes (perceived stress, depression and anxiety) via the mindfulness facets (describing, acting with awareness and non-judging)
As can be seen in Table 4
, only the non-judging
facet of mindfulness operated as a partial mediator for the effect of the intervention. The direct pathway (F’, see Table 3
) remained significant with the mediators in the model suggesting some remaining unexplained variance. The bias corrected bootstrap confidence interval for the indirect effect of non-judging
on perceived stress (95% CI [− 4.33, − 0.61]) did not include zero; therefore, this was a significant effect.
The model explaining the effect of the intervention on depression was more complex. As can be seen in Table 4
, both non-judging
appear to have operated as mediators for the effect of the intervention on depression, although the effect for describing
was smaller than that for non-judging
. Bias corrected bootstrap confidence intervals for the indirect effects of non-judging
(95% CI [− 3.06, − 0.30]) and describing
(95% CI [− 1.00, − 0.02]) on depression did not include zero; therefore, these were significant effects. Furthermore, the direct pathway was no longer significant with the mediators in the model suggesting this was a full mediation effect.
Finally, with respect to anxiety, Table 4
shows that only the non-judging
facet of mindfulness operated as a mediator. Bias corrected bootstrap confidence intervals for the indirect effect of non-judging
on anxiety (95% CI [− 2.75, − 0.13]) did not include zero; therefore, this was a significant effect. As the direct pathway was no longer significant with the mediators in the model, this represented a full mediation effect.
Analysis of Change over Time
We assessed the effect of the intervention over time for the outcome variables for the intervention group and for the waitlist control group separately. The waitlist control group completed the intervention after the waitlist period and were also followed-up 3 and 6 months after they completed the intervention. We were interested to see if waitlist control participants reported improvements that were similar to those reported by intervention participants. Table 5
shows that, for both groups, there was a significant main effect of the mindfulness intervention over time for all of the outcome variables (with large effect sizes; Cohen 1988
). Furthermore, for all outcomes—when compared to baseline scores—the differences at post-treatment, 3- and 6-month follow-up were significant and were also associated with large effect sizes (Cohen 1988
Intention-to-treat and per-protocol repeated measures ANOVA results and within group effect sizes for outcome variables for intervention and waitlist control groups
Perceived stress (main effect)
T1 vs. T2
T1 vs. T3
T1 vs. T4
Depression (main effect)
T1 vs. T2
T1 vs. T3
T1 vs. T4
Anxiety (main effect)
T1 vs. T2
T1 vs. T3
T1 vs. T4
Clinically Significant Change
Chi square tests showed a significantly smaller proportion of participants allocated to the INT group, as compared with those allocated to the WLC group, continued to report moderate/severe levels of depression and anxiety immediately after the intervention was completed (see Table 6
). Based on the odds ratio, the odds of participants in the WLC group reporting moderate/severe depression and anxiety were six to seven times higher than participants in the INT group immediately after the mindfulness intervention had been completed. For perceived stress, we assessed the post-treatment scores for each group against the normative mean for the PSS-10 (X
= 13.02; Cohen et al. 1983
; Cohen and Williamson 1988
), and found that while both groups reported perceived stress levels which were significantly higher than the normative mean (WLC: X
= 22.41, t
 = 10.204, p
< 0.001; INT: X
= 14.57, t
 = 2.197, p
= 0.03), the mean PSS score in the intervention group was approaching the normative value at the end of the intervention.
Intention-to-Treat and Per-Protocol Analyses of the Proportion of Participants in the Intervention and Waitlist Control Groups meeting criteria for moderate to severe levels of anxiety and depression at post-intervention
Impact of Course Completion Time
Participants were encouraged to complete the course within 4 weeks of their start date; however, there was variation with regards to time taken to complete the course. The average time participants in the intervention group took was 6 weeks and 3 days, and all had completed the course within 12 weeks. In detail, 11.1% (n = 5) completed within 4 weeks, 62.2% (n = 28) completed within 6 weeks, 84.4% (n = 38) completed within 8 weeks, 95.5% (n = 43) completed within 10 weeks and 100% (n = 45) completed within 12 weeks. In order to assess whether there were differences in the effect of the intervention due to time taken to complete the course, data from participants in the intervention group was split into those who completed within 6 weeks (n = 30), and those who took longer than 6 weeks to complete (n = 15). A series of t tests were performed and results showed no significant differences between those who completed the course within 6 weeks and those that took longer than 6 weeks for any of the study outcomes.
Results showed that participants who completed the online mindfulness course reported significantly lower levels of perceived stress, depression and anxiety. The large effect sizes associated with completing the intervention were maintained for all of the outcome variables at 3- and 6-month follow-up. The effect sizes in this study rival those of studies which have employed a group-based face-to-face format for mindfulness-based intervention delivery (e.g. see Nyklicek and Kuijpers 2008
), and they align with the findings from Krusche et al. (2012
) in their pre-post study design. However it is important to note that the relatively high baseline levels reported in this sample meant there was more capacity for change from baseline, and our results are contrary to the small (depression, anxiety) and medium (stress) effect sizes reported in the recent meta-analysis by Spijkerman et al. (2016
). Nonetheless, it is possible these differences are a reflection of the different online mindfulness interventions being assessed. For example, all of the studies included in Spijkerman et al.’s meta-analysis were MBSR or Acceptance and Commitment Therapy (ACT), whereas the intervention assessed in this study was an MBCT intervention. Perhaps MBCT has proven more effective when operationalised online than the other mindfulness-based interventions. However, this is speculative and further empirical work is needed. In addition, Spijkerman et al. included studies with student, general population and clinical samples; therefore, the reported effect sizes for depression, anxiety and stress may have been influenced by differences conferred by the different sample types.
A number of authors have called for research designed to understand by what mechanism/s mindfulness exerts its positive influence (e.g. Brown et al. 2007
; Glomb et al. 2011
). Our results showed that the online mindfulness course exerted its effect on the outcome variables predominantly through increased levels of one facet of mindfulness; that is, increased levels of non-judging
did contribute to the model for depression). While the intervention worked to increase levels of other facets of mindfulness (acting with awareness and describing
), these facets did not mediate the change in the outcome variables, and non-reacting
did not appear to be affected by the intervention. These findings are of interest for a number of reasons. It is curious that the mindfulness intervention did not affect all of the mindfulness facets, and two other studies have shown similar findings. From the occupational health literature, Querstret et al. (2016
) found that three out of the four mindfulness facets were affected by the intervention (acting with awareness, describing, and non-judging); however, only one facet (acting with awareness) mediated the change in work-related rumination, fatigue and sleep quality. From the clinical literature, Boden et al. (2012
) found that the impact of their intervention on post-treatment posttraumatic stress disorder severity was mediated by acting with awareness
; whereas, the impact on post-treatment depression severity was mediated by non-judging
. These differing findings raise an interesting possibility that the different facets of mindfulness are more or less important with regards to their impact on different health outcomes.
If only some of the mindfulness facets are implicated in mediation models perhaps interventions targeting those facets would be useful. However, this is a cautious proposal as more research is needed to understand how the different facets relate to one another. For example, Querstret et al. (2016
) posited that some facets may develop earlier in mindfulness training (e.g. observing, describing and acting with awareness), with the remaining facets developing when participants are more skilled (e.g. non-judging, non-reacting). If this is the case, it might be that study designs are not long enough to capture the change in non-reacting (for example) because it may develop though continued practice after the study has ended.
Our study was conducted in a general population sample; however, in both study groups approximately half the sample reported moderate to severe depression and anxiety at baseline. All participants were working at the time of taking part in the study suggesting a relatively high level of functioning. In the context of research suggesting that much of the burden of disability in the population is attributable to subclinical symptoms (Judd et al. 2002
); intervening early before depression and anxiety increase to clinically diagnosable levels could be beneficial for the individual (i.e. by keeping them in work and feeling productive and healthy) and to health services, by reducing the number of people needing to engage with more complex psychological therapy and other forms of intervention (e.g. drug therapy). Therefore, operationalising therapies (like mindfulness) online could increase their availability, reduce waitlist times and reduce cost to health services.
An inherent limitation in waitlist control designs is that they do not allow for multiple treatments to be assessed against each other; therefore, the effects in this study may reflect a general treatment effect. However, the effect sizes in this study are comparable to those in studies considering mindfulness in randomised controlled trails (e.g. van Aalderen et al. 2012
; Vollestad et al. 2011
). Data concerning the amount of meditative practice participants engaged in over the course of the study was not collected which makes it difficult to assess whether the amount of practice participants engaged in was a mechanism of change. For example, the moderate to large effect sizes found in the current study may be an artefact of a very motivated cohort, practicing consistently many hours and days a week.
The moderate to severe levels of self-reported depression and anxiety in both groups at baseline does raise questions about the generalisability of our findings to other general population samples. We did not seek to recruit a clinical sample; however, many of our participants were recruited from industry sectors which may be inherently stressful to work in (e.g. healthcare, education, financial services, information technology, telecommunications). It is also more likely that individuals experiencing higher levels of distress would be more attracted to an intervention for health and wellbeing, so the baseline levels may also reflect a tendency for individuals who need intervention to self-select into these types of studies. The compensation offered to participants for taking part in the study (£50 worth of shopping vouchers) was not insubstantial and may have kept participants engaged in the study, masking the true dropout rate. It may also have influenced the generalisability of the sample with motivation for taking part being linked to the reimbursement.
Related to issue of large effect sizes, the current study has demonstrated some significant mediation effects with a relatively modest sample size (n
= 118). However, the failure to detect more modest mediation effects may have been the result of relatively low power for such complex mediational analyses rather than the effects themselves not existing (see Fritz and MacKinnon 2007
). This is clearly an empirical question for future research so it is premature to conclude that only non-judging is the active ingredient in mindfulness interventions of this sort. Finally, we need to exercise caution in claiming causal mediating relationships since assessment of change was based on changes in variables measured at the same time points. We cannot entirely rule out the possibility that changes in our outcome variables caused the changes in our putative mediators.
Given the findings in this study showing the only one facet of mindfulness (non-judging
) predominantly accounted for the effects of the intervention on the outcome variables, it would be useful to replicate this study in different samples to assess the stability of these findings. It would also be useful to conduct other studies with varying outcome variables, from different health domains, to further understand if the different mindfulness facets are specifically related to different conditions or health domains. This could then enable the development of interventions that are also condition/domain specific. Ideally, future mediation studies should attempt to show that changes in the mediators occur temporally prior to changes in the outcomes. For example, Kazdin (2007
) recommends that both mediators and outcomes are measured several points throughout treatment to establish whether the mediator changes prior to any change in the outcome variable(s). Furthermore, because the results showed no difference between participants who took less than 6 weeks to complete the course and those who took longer than 6 weeks, developing shorter interventions may be fruitful. Further empirical work is needed with larger RCTs and well-chosen active and inactive control groups in order to understand the generalisability, implementation challenges, and cost-effectiveness of the intervention assessed in our study. Further empirical work assessing online mindfulness interventions against face-to-face group-based mindfulness interventions is also warranted to understand the relative contribution of social support offered in group-based formats.
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