Background
Youth are disproportionately represented in epidemiological studies of anxiety and depressive disorders [
1]. Furthermore, evidence suggests that 50% of these disorders begin before the age of 14 and 75% by age 24 years [
2]. Anxiety and depressive disorders significantly impact on individuals, their families, workplaces, communities, and countries [
3‐
5], making prevention an important goal. Compared to treatment in the early stages of the disorder, termed ‘early intervention’, prevention averts the short- and long-term consequences of such disorders and has been shown to be more cost-effective [
6,
7]. Prevention programs that are delivered to all individuals irrespective of their level of symptomatology, termed ‘universal prevention’, reduce the logistical difficulties involved in large-scale screening, avert missing susceptible students, and ensure that the benefits of such a program are available to all. Existing prevention programs have largely drawn these skills from cognitive behavioural therapy (CBT), which focuses primarily on teaching individuals to change their appraisal of a situation in order to modify the emotional experience [
8‐
11].
Mindfulness, a particular manner of engaging with one’s environment, is a concept that has grown in popularity over recent years. It has been defined as comprising two components—paying attention to the present moment and doing so with a non-judgmental attitude [
12]. These two components correspond closely with two well-established emotion regulation strategies: attention deployment and acceptance [
13,
14]. Attention deployment is the ability to choose which aspect of a situation to focus on while acceptance involves allowing an emotion to occur without attempting to avoid the experience. With emotion regulation implicated in the development of mental disorders, particularly to anxiety disorders and depression [
14‐
17], it is unsurprising that numerous clinical trials have demonstrated that mindfulness can assist with a wide range of mental health symptoms in adult populations [
18‐
28].
There are reasons to believe that mindfulness may be beneficial to adolescents in navigating their environment. Developmental brain changes mean that adolescents are more impacted by emotions than adults or children: they have increased limbic reactivity (indicative of a greater sensitivity to threat), a stronger startle reflex (suggesting a more intense automatic emotional reactivity), and are more interfered by emotional stimuli when completing tasks [
29‐
32]. In spite of adolescents experiencing stronger emotional reactions, the frontal lobe of the brain, which controls the executive functions such as judgment, impulse control, planning, and emotion regulation, remains underdeveloped [
33]. Mindfulness and its ability to regulate emotions, may help counteract this imbalance. Research has demonstrated that mindfulness can reduce mental health symptoms in both clinical and non-clinical adolescent populations [
34].
There are a number of existing programs that have been designed to train individuals to become more mindful such as mindfulness-based stress reduction (MBSR), mindfulness-based cognitive therapy (MBCT), and acceptance and commitment therapy (ACT). MBSR has a focus on teaching meditation practices, which serve to train the brain to become more mindful (similar to using weight training to increase physical strength). MBCT combines meditational practices with components of cognitive-behavioural therapy for depression. Unlike MBCT and MBSR, ACT does not use meditation but rather is didactic in style and draws heavily on imagery, metaphors, personal stories, and short experiential exercises. It also focuses on the application of mindfulness to emotions and related internal constructs such as thoughts, memories, and body sensations. In addition to mindfulness, ACT draws on the concept of ‘values’ as an over-arching framework to guide the intervention techniques, improve life-satisfaction, and increase motivation. ACT defines values as the type of person an individual wishes to be in the future. Behavioural principles are also incorporated into ACT to assist a person in working towards their values. Engaging in such behaviours that are important and goal-directed even while experiencing intense emotions, may be regarded as a form of emotion regulation [
35]. Acceptance principles are encouraged when thoughts and feelings draw the individual away from maintaining value consistent behaviours. ACT does not distinguish between psychopathology and everyday struggles and so, is equally applicable to those with or without significant psychopathology. While ACT was developed for adults, it has been successfully applied to adolescent clinical populations [
36‐
38]. When used with adolescents, ACT principals remain the same but exercises, examples, and metaphors employed will be more age appropriate [
39].
Acceptance and commitment therapy is an appealing mindfulness program to use with adolescents compared to other meditation-based programs because adolescents may struggle to engage with meditation, particularly in a school setting. It is also appealing for use with adolescents as it places particular emphasis on using mindfulness to regulate emotions, which is important for this age group. Finally, the additional components of ACT such as values may be particularly useful for adolescents as they are in an important transitional period where they are creating a self-identity. ACT has been shown to be effective in clinical samples of adolescents to address symptoms of depression and anxiety [
37,
38] but remains untested as a prevention program (i.e. in a non-clinical sample of adolescents). The results from clinical samples suggest that ACT is effective as an emotion regulation strategy and so is worth evaluating as a prevention program. There are nonetheless differences in using ACT as a therapy compared to as a prevention program. Many ACT-based therapies will incorporate other elements to target the disorder (e.g. behavioural activation for depression or exposure for anxiety) whereas in prevention this may be less relevant. Instead it may be more important to emphasise how experiential avoidance can lead to many types of problems and techniques that can be used to reduce experiential avoidance. Furthermore, the examples used to illustrate how ACT can be applied to real-life situations in clinical therapies may need to be modified to make ACT more relevant to a non-clinical population.
The present study sought to investigate for the first time an ACT-based intervention as a school universal prevention program. One problem in the evaluation of a new prevention program is the issue of statistical power. Given there is a low rate of emergence of new cases of anxiety and depression over any given period, it has been estimated that over 30,000 participants are needed to adequately power a prevention program evaluation study [
40]. Measuring symptom reduction rather than cases can reduce this figure but still almost 1000 would be required to demonstrate a statistically significant difference between conditions [
41]. However to justify investment in a trial of this size, preliminary evidence, obtained in a feasibility study, is required. The aims of this study were to: (a) examine the feasibility and acceptability of using an ACT-based prevention program that targets anxiety and depressive symptoms in a non-clinical sample of adolescents; and (b) to compare the impact of the ACT-based program on wellbeing and symptoms of depression and anxiety. It was expected that there would be a trend for the ACT participants to demonstrate improvements on a range of measures compared to participants in the control condition. Given the underpowered nature of feasibility studies, this trial sought to use effect sizes as an indication of feasibility and to provide evidence to determine whether a large-scale prevention study of this intervention would be appropriate.
Results
Mean scores and standard deviations for the ACT and control condition are presented in Table
2.
Table 2
Means (SDs) for mental health measures at each time point, N = 48
DASS-depression | ACT | 7.34 (7.85), n = 17 | 7.38 (6.81), n = 15 | 6.00 (5.59), n = 12 |
Control | 9.27 (10.95), n = 31 | 12.33 (12.25), n = 19 | 11.25 (10.75), n = 16 |
DASS-anxiety | ACT | 9.06 (7.22), n = 17 | 8.00 (6.55), n = 15 | 5.33 (4.03), n = 12 |
Control | 9.42 (8.47), n = 31 | 10.63 (9.59), n = 19 | 10.19 (10.08), n = 16 |
DASS-stress | ACT | 13.29 (7.87), n = 17 | 11.07 (6.32), n = 15 | 9.00 (5.62), 12 |
Control | 11.48 (8.75), n = 31 | 14.70 (11.17), n = 19 | 13.63 (9.75), n = 16 |
DASS-total | ACT | 29.78 (20.99), n = 17 | 26.44 (16.75), n = 15 | 20.33 (12.26), n = 12 |
Control | 30.17 (25.57), n = 31 | 37.67 (29.72), n = 19 | 35.06 (28.48), n = 16 |
FS | ACT | 46.47 (7.19), n = 17 | 46.64 (9.47), n = 14 | 45.64 (7.12), n = 11 |
Control | 44.45 (7.40), n = 31 | 43.11 (9.80), n = 19 | 41.30 (8.36), n = 15 |
Baseline comparisons
The comparison of baseline scores of the ACT and control conditions found no significant differences for DASS-depression (p = .55), DASS-anxiety (p = .88), DASS-stress (p = .48), DASS-total (p = .96), or FS (p = .37). No significant difference in sex distribution was found between the conditions (p = .72).
Comparison of dropouts
Comparisons of the differences between participants that completed their post-intervention and follow-up questionnaires (‘completers’) from those who did not (‘dropouts’) suggested there were no significant differences between post-intervention completers and dropouts on DASS-depression (p = .69, Cohen’s d = .14), DASS-anxiety (p = .88, Cohen’s d = .05), DASS-stress (p = .72, Cohen’s d = .11), DASS-total (p = .81, Cohen’s d = .08), and FS (p = .93, Cohen’s d = .02). Likewise, no differences were found between follow-up dropouts and completers scores for DASS-depression (p = .36, Cohen’s d = .27), DASS-anxiety (p = .18, Cohen’s d = .41), DASS-stress (p = .29, Cohen’s d = .33), DASS-total (p = .24, Cohen’s d = .36), and FS (p = .28, Cohen’s d = .32). No significant differences were detected on the variable sex between the completers and dropouts at post-intervention (p = .67, φ = .11) or follow-up (p = .92, φ = .06). Likewise, no differences in attrition were observed between the ACT and control conditions at post-intervention (p = .10, φ = .27) or follow-up (p = .20, φ = .18).
Universal effects of the program
The MMRM findings from the Time × Condition analyses are presented in Table
3. There were no significant differences between the ACT and control conditions for the DASS-21 or FS. However, given this was a pilot study in a non-clinical sample, we were chiefly interested in whether effect sizes suggested that a larger trial of the intervention would be worthwhile. Effect sizes were calculated for both baseline-post and baseline-follow-up differences. Table
4 presents Cohen’s
d effect sizes observed for the difference between the ACT and control conditions. Results indicate medium or large between-group effect sizes for all outcomes for baseline to follow-up differences.
Table 3
Linear mixed modelling time × condition results, type III fixed effects, N = 48
DASS-depression | 1.61 | .24 | .79 |
DASS-anxiety | 1.60 | 1.72 | .19 |
DASS-stress | 1.61 | 2.05 | .14 |
DASS-total | 1.60 | 1.39 | .26 |
FS (Wellbeing) | 1.45 | .57 | .57 |
Table 4
Cohen’s d effect sizes and standard interpretations, N = 48
DASS-depression | .31 | Small | .34 | Medium |
DASS-anxiety | .28 | Small | .55 | Medium |
DASS-stress | .63 | Large | .75 | Large |
DASS-total | .44 | Medium | .59 | Medium |
FS | .20 | Small | .31 | Medium |
Program evaluation
Twenty-four participants, from both conditions, completed the ACT program evaluation. Program evaluation data are summarized in Table
5. To assess the percentage of affirmative/negative responses, the ‘Strongly Disagree’, ‘Moderately Disagree’, and ‘Slightly Disagree’ responses were combined into a single outcome ‘Disagree’ and the same done for the three agree options which were combined into ‘Agree’. Overall, there was agreement with the questions posed, except in response to whether they were exercising more.
Table 5
Means and percentage of participants agreeing on the program evaluation questions, N = 24
More confident | 24 | 4.1 | 1.4 | 75 |
Less impact of negative thoughts | 23 | 4.0 | 1.2 | 70 |
Happier | 24 | 4.0 | 1.7 | 67 |
Workshops helpful | 24 | 3.8 | 1.4 | 63 |
More comfortable with negative emotions | 24 | 3.8 | 1.1 | 63 |
Values clearer | 24 | 3.6 | 1.6 | 58 |
Better relationships | 24 | 3.5 | 1.8 | 54 |
Less impacted by anxiety | 24 | 3.5 | 1.7 | 50 |
Applying workshops to everyday life | 24 | 3.6 | 1.2 | 50 |
Exercising more | 24 | 2.5 | 1.7 | 29 |
Discussion
The current study investigated the feasibility of using an ACT-based prevention program for adolescents in a school setting. As expected because of the small sample size, the analyses indicated that there were no statistically significant differences between the ACT and control conditions on the outcome measures of depression, stress, anxiety, total negative affect, and wellbeing. The effect sizes, which were expected to be of greater utility in this study, ranged from small to large according to Cohen’s standards [
57], all in the direction of greater improvements in the ACT compared to control condition. The high rate of endorsement of the various items in the workshop evaluation questionnaire also suggests that many participants perceived benefits from the workshops. To our knowledge, this is the first time that an ACT-based program has been evaluated as a prevention program in a non-clinical population of adolescents. It is conceivable that with a larger sample size, a universal prevention evaluation study of an ACT-based program may find mean differences that are statistically significant.
Interestingly, the present study found that stress scores demonstrated greater improvements over time than anxiety scores on the DASS-21. While both are broad measures of anxiety, the stress scale of the DASS-21 relates to cognitive symptoms (i.e. worry) while the anxiety subscale tends to relate to physiological symptoms (e.g. increased heart beat). Given that worry may be regarded as a form of avoidance [
58], it is unsurprising that this aspect would be more amendable to change for participants in the ACT intervention compared to physical symptoms that are not associated with avoidance behaviours.
Compared to the findings from CBT prevention programs, our results are encouraging. A meta-analysis of prevention programs for depression [
10] found that the average effect size from baseline to post-intervention was Pearson’s
r = .15 (Cohen’s
d = .30), which is equivalent to our results. Effect sizes at follow-up were Pearson’s
r = .11 (Cohen’s
d = .20), which is lower than the effect size found in the present study. Early intervention programs targeting depression and other mental health-related problems have reported a reduction in efficacy from post-intervention to follow-up [
10,
59]. These programs were predominately CBT-based and thus focused on teaching skills, the retention of which is likely to diminish over time. The present intervention, on the other hand, observed an increase in efficacy from post-intervention to follow-up. It is possible that ACT may create a more fundamental shift in how a person relates to their thoughts and feelings rather than teaching a new set of skills [
60].
The program evaluation questions showed strong satisfaction with the ACT program. The item which most students agreed with related to increased confidence from the workshops. This is likely to reflect that many young people struggle with low confidence. Despite two-thirds of participants reporting that the workshops were helpful, three-quarters said they felt more confident because of them, which may be reflective of a tendency amongst adolescents to downplay positive changes.
The present study used a large group setting to deliver the workshops, with approximately 60 students attending the workshop at the same time. The findings suggest that future early intervention programs may not need to be delivered to small groups. Large groups enable programs to be more readily delivered by external psychologists (due to reduced costs) rather than teachers which is an important advantage given that research suggests that compared to teacher-led programs, psychologist facilitated programs have better outcomes [
59,
61]. In addition, it was observed that in the present study, students asked clarifying questions on the workshop material that schoolteachers without psychology training/experience would have difficulty in answering. The responses to these questions appeared important to ensure students understood the material taught. For these reasons, we recommend that trained psychologists rather than schoolteachers deliver the program.
This study did have a number of methodological issues that limit the conclusions that can be drawn, including the small sample size and the quasi-randomisation process. Although the randomisation method led to unequal numbers of participants in each condition, importantly, baseline differences between conditions were not statistically different. Another limitation was the inability to differentiate the benefits obtained from the practical teacher-led exercises compared to the psychologist-led workshops. Future research to examine their differential benefits would be of interest. The study was also limited in that the sample used was a private school with students from high socio-economic status families. It would be of interest to evaluate the program across the socio-economic spectrum. The present study experienced a substantial dropout of participants in the control condition between baseline and post-intervention. The workshops ended close to school holidays and so the limited time available before students left meant that the students in the control condition, absent on the day the questionnaires were administered, could not be located. This learning can be utilised in future school-based program evaluation research to avoid this same issue.
There are a number of components that would be of benefit to include in a larger trial of an ACT-based prevention program. Examining an increased range of outcomes, such as academic indicators and social relationships (e.g. family, friendships, teacher–student) in addition to the mental health outcomes, would be of interest. The study design could also have been improved by including a measure of emotion regulation, and it is recommended that future studies in this area do so. In addition, it would be of benefit that such a trial test the model that mindfulness reduces and prevents depressive and anxiety symptoms through improved emotion regulation. Including mediator variables and testing this model through analysis would provide greater insight into the link between mindfulness and symptom reduction/prevention. Future trials could also be strengthened by examining potential confounds and moderators of outcome, such as previous experience with mindfulness, current engagement with mental health professionals, student tutorial group, school exams during the study period, and past engagement with mental health prevention workshops. Finally, although it would be resource intensive, a future trial that can compare the effectiveness of several key emotion regulation strategies (e.g. problem-solving, cognitive re-appraisals, and acceptance) as well as a combined program of all these together, would be of great benefit to the field of prevention.
Authors’ contributions
RB and VM designed the intervention; RB delivered the intervention, developed the fidelity scale, collected the data, analysed the results, and wrote the manuscript; PJB and DH-P advised on statistical analysis; RB, VM, PJB, and FS contributed to editing the manuscript. All authors read and approved the final manuscript.