This was a prospective, three arm (experimental treatment, standard treatment and a control group without treatment), randomized, controlled trial with three assessment time points (baseline, post-intervention and follow-up one year post-intervention). This design was created in order to analyze both short term and long term effects while examining potential effects of the training in comparison to the waitlist control group and standard treatment with Autogenic Training.
According to the description in the study protocol , a sample size of 126 participants at the 5-year follow-up was calculated leading to an initial sample size of 189 participants. Related publications [20, 23, 26] used different designs and statistical approaches, with non-randomization or experimental vs. wait-list control group design. This lead to a synopsis, integration and analysis with effect sizes of the different outcome measures (F-values respective η-square-values, Cohen’s d  and Λ for multivariate approaches) with G*Power  and power calculation with 80% .
This trial received approval from the local ethics committee (Landesärztekammer Rheinland-Pfalz, file number: 837.380.13/9065-F) and the University Medical Center data protection official. All participants provided written informed consent according to the 1964 Helsinki declaration and its later amendments.
The study was offered to medical students in the second and eighth semester of the Johannes Gutenberg University in Mainz (Germany). Because the curriculum and learning environment of dental students in the preclinical semesters is nearly analogous to that of medical students, dental students in their second semester were also included. The trainings (MediMind and Autogenic Training) were provided as a voluntary extra-curricular activity and students were introduced to the study design and the opportunity of participation at lectures and by written information. In order to secure privacy, students were informed that all health data was strictly secured and held separately from their medical faculty. The signed informed consent was a requirement to take part in the baseline assessment. At the post-intervention assessment time point, 50.- € vouchers were raffled among the participants as an acknowledgment of their participation. As a motivating incentive the participants of the control group received a 20.- € voucher. Because of the low response rate, everyone who participated in the follow-up assessment received a 20.- € voucher.
The recruitment started in November 2013. Unfortunately, due to study limitations, the recruitment had to be terminated before full sampling had been completed.
Interventions and trainers
The training was parallelized in both treatment groups and each intervention was presented over a period of five weeks with weekly sessions of 90 min. This also included the provision of an accompanying booklet or handout to the participants containing the contents of each training session and the instructions for practice assignments. The treatment groups were led by a total of four trainers (clinical psychologists, licensed in psychotherapy with relevant experience in mindfulness interventions, and one physical education instructor certified as a trainer of Autogenic Training). Two of the trainers led MediMind and the other two trainers the Autogenic Training. There was no change between the trainers. The staff was instructed in the intervention trainings and followed a comprehensive operation manual. Participants of the control group remained without treatment but participated in the assessment time points. MediMind will be offered to them when the five-year follow-up assessment is completed.
A detailed description of the trainers’ qualifications as well as the contents and sequence of trainings (MediMind and Autogenic Training) is published in the study protocol .
Mindfulness-based stress prevention training for medical students (MediMind)
In order to develop an intervention program tailored to the needs of students in medical education, interviews with the target group were conducted beforehand. Students often mentioned the need to acquire specific action-oriented strategies to help them face stressful situations, such as examinations or high workload. This was taken into consideration when developing MediMind and combining mindfulness aspects with approaches from cognitive behavioral therapies. This implies learning how to relate to one’s own experiences in a more accepting and non-judgmental way, and helps one not to be overwhelmed by thoughts and feelings. Therefore, mindfulness meditation was practiced in each training session and CDs were provided for home practice. The participants were introduced to the ‘satellite-position’ as a target state of mindfulness and learned how to observe thoughts, emotions, physical reactions and impulse to act. In exercises, they became familiar with the presence-of-mind attitude in order to realize and target stress constructively. In this context, participants learned to address intrusive and distracting thoughts and feelings in an accepting attitude in order to feel less involved and to reduce their stressful impact. Another concept known to be effective in preventing stress is represented by the approaches of cognitive behavioral therapy . This focuses on the stress heightening influence of dysfunctional cognitive judgment mechanisms and follows the approach of change and action-oriented strategies that do not require long-term training and work as skills in dealing with stressful situations. In this context, the students became aware of the impact of cognitive judgment mechanisms and core beliefs (‘I always have to perform perfectly!’) on our feelings and level of stress. This was taken into account by additionally implementing stress-management techniques of the cognitive behavioral therapies to our training. The participants learned how to detect dysfunctional cognitive judgment mechanisms (errors in reasoning) and practice the use of functional reevaluation. Additionally, the stress heightening influence of personal standards and assumptions were discussed. The students were introduced to various experiments in order to find a health-promoting way of dealing with these personal standards and assumptions. To cope with tense situations, the use of stress-tolerance skills and the concept of radical acceptance was imparted .
The combination of acceptance strategies (concept of mindfulness) with change strategies (contents of cognitive behavioral therapies) enabled the participants to be less reactive when experiencing stress and to decide more deliberately whether change is possible. This offered the possibility to either modify the situation, adapt their judgment mechanisms, or to otherwise meet these conditions with acceptance. This combination follows the concept of dialectical behavior therapy developed by Linehan . The extension of mindfulness involving strategies to change dysfunctional cognitive assessment-mechanisms is also described in Lehrhaupt & Meibert  and Hassed et al. . Practice assignments helped to generalize the effects of the training and to apply the techniques in everyday situations.
The basic skills of Autogenic Training according to the Schulz method  were practiced in this intervention group. As it is an auto-suggestive relaxation technique, the participants learned how to instruct themselves to suggest specific autonomic sensations such as muscular relaxation, vascular dilatation, stabilization of heart function or regulation of breathing . These instructions consist of six exercises with corresponding formulas that are subvocally repeated (e.g. ‘My arm is very heavy’). Additionally, the training is extended by exercises including progressive muscle relaxation, breathing relaxation, exercises for body awareness, imaginary journeys and qigong movements. Individual practice outside the training was supported by informational material.
In the present study, we report the results of three assessment time points: (1) baseline, after receiving signed informed consent and before random assignment to the study groups; (2) post intervention, three weeks after the last training session; (3) follow-up, one year post trial. At each assessment time point, data of the primary, co-primary and secondary outcome measures were collected. Standard demographic measures were assessed at baseline. Additionally, at post intervention and follow-up assessment participants were asked to assess how often per week they used the strategies that were taught in the trainings.
Primary outcome measure
Trier Inventory for the Assessment of Chronic Stress (TICS) . The TICS consists of 57 items to evaluate different aspects of chronic stress by assessing nine subscales: ‘work overload’, ‘social overload’, ‘excessive demands from work’, ‘lack of social recognition’, ‘work discontent’, ‘social tension’, ‘pressure to perform’, ‘social isolation’ and ‘chronic worrying’. The answers are rated on a Likert-type scale ranging from 0 (‘I never experienced this’) to 4 (‘I experienced this very often’). In order to assess the experience of chronic stress, an additional Chronic Stress Screening Scale (SSCS) can be computed that consists of 12 items taken from the other dimensions (‘chronic worrying’, ‘work overload’, ‘social overload’, ‘excessive demands from work’ and ‘lack of social recognition’). Cronbach’s α ranged from .84 to .91 and is classified as good to excellent. Validity was confirmed by a principal component analysis resulting in a nine-factor solution and plausible correlations between the TICS and other stress questionnaires .
Co-primary outcome measure
Brief COPE . The Brief COPE assesses 14 dimensions of effective and ineffective coping strategies: ‘self-distraction’, ‘active coping’, ‘denial’, ‘substance use’, ‘use of emotional support’, ‘use of instrumental support’, ‘behavioral disengagement’, ‘venting’, ‘positive reframing’, ‘planning’, ‘humor’, ‘acceptance’, ‘religion’ and ‘self-blame’. It consists of 28 items with four response categories of a Likert-type scale ranging from 1 (‘not at all’) to 4 (‘very much’). Cronbach’s α range from .50 to .90 and reflects poor to good internal consistency. Construct validity could be confirmed by a nine-factor solution similar to the full inventory . Convergent and discriminant validity is confirmed by plausible correlations between coping strategies and personality qualities . The Brief COPE is available in a German translation and has been validated .
Secondary outcome measure
Brief Symptom Inventory (BSI) . The BSI measures psychological distress based on nine subscales: ‘Obsessive-Compulsive’, ‘Paranoid Ideation’, ‘Hostility’, ‘Somatization’, ‘Depression’, ‘Interpersonal Sensitivity’, ‘Anxiety’, ‘Psychoticism’ and ‘Phobic Anxiety’. It consists of 53 items to be answered on a Likert-type scale ranging from 0 (‘not at all’) to 4 (‘extremely’). A global measure of overall psychological distress is provided as an average response on each item (Global Severity Index; GSI). A German version is available and internal consistency coefficients (Cronbach’s α) show good results ranging from .70 to .88 in a community sample. Validity is proven by plausible correlations between the BSI and other instruments .
After signing informed consent and baseline evaluation, participants were randomized to one of the three study groups (MediMind, Autogenic Training or control group) . In order to control for potential confounding effects, students were stratified randomized by course of study (medical versus dental), semester (2nd or 8th) and sex. Regarding maximum power for analysis between experimental versus standard treatment, an allocation ratio with 2 (MediMind) : 2 (Autogenic Training) : 1 (control group) was realized. Randomization was operationalized via drawing lots by an independent member of the institute not involved in the project.
All analyses (except sample size calculation as stated above) were conducted using IBM SPSS Statistics, Version 23. A p-value of < .05 with an α-level of 5% set for statistical significance. Following a conservative procedure, reducing potential α-errors when imputing data , the two-folded approach  stated in the study protocol was reduced to a completer-analysis including all persons with complete data-sets.
Descriptive data at baseline was further analyzed with t-tests for metric variables and X2-tests for binary variables, respective Fisher’s Exact Test if expected cell frequency was less than five . Differential analysis with t-tests of missing data, response, drop-out rates and time of post-data collection were used to access potentially confounding effects.
All metric variables were tested for normality via Kolmogorov-Smirnoff-Tests  resulting in non-normality in the secondary outcome and normalization via logarithmic transformation of the data .
In order to reduce multiple testing with familywise Type I errors  for primary, co-primary and secondary outcome, MANCOVA’s with group x time interactions and the covariates gender and time of post-data collection (due to differences stated below) were performed. Post hoc MANCOVA’s were applied with Bonferroni-Holm  corrections for multiple testing regarding differential interactions between MediMind and control group and MediMind and Autogenic Training. Separate scales of the instruments for the outcomes were tested in post hoc repeated measures ANCOVA’s with Bonferroni-Holm correction.
Partial η-square values according to Cohen  were calculated for estimating effect sizes referring to interaction effects with cut-off-norms of η-square values ≥ .0099 denoting to a small effect size, η-square values ≥ .0588 denoting to a medium effect size and η-square values ≥ .1379 pointing to a large effect size.