Self-administered Mindfulness Interventions Reduce Stress in a Large, Randomized Controlled Multi-site Study
Phase: NA
Conditions: Body Scan Meditation, Loving-Kindness Meditation, Mindful Breathing Meditation, Mindful Walking Meditation, Control Condition
Sponsor: Swansea University

Date: 22 March 2022; Swansea University (UK) & Université Grenoble Alpes (France) 
Self-administered mindfulness interventions reduce stress in a large, randomized 
controlled multi-site study  
 
Alessandro Sparacio1,2, Hans IJzerman1,3, Ivan Ropovik4,5, Filippo Giorgini6, Christoph 
Spiessens7, [authors that contributed with the data collection with at least 70 participants], 
Gabriela M. Jiga-Boy2 
 
1Université Grenoble Alpes, 2Swansea University, 3Institut Universitaire de France, 4Charles 
University in Prague, 5Presov University, 6University of Milano-Bicocca, 7Christoph 
Spiessens Coaching Solutions Ltd. 
 
 
 
 
 
 
 
 
 
 
This project was pre-registered on March 22th, 2022. For any further changes, please 
contact Alessandro Sparacio 
 
Author Note: Note that we wrote the pre-registration in past tense to avoid errors after 
finishing the manuscript. Our OSF page can be found here (https://osf.io/6w2zm/) 
 
 

Date: 22 March 2022; Swansea University (UK) & Université Grenoble Alpes (France) 
Abstract 
The use of self-administered mindfulness interventions has increased in recent years. The 
effectiveness of these interventions on regulating stress/emotions, however, is debated. In the 
present multi-site study (Nsites = x, Nparticipants = x), we aimed to investigate the effectiveness of 
four single, brief stand-alone mindfulness exercises in a population unfamiliar with 
mindfulness meditation. We tested these four interventions in comparison to non-mindful 
active control conditions using an adaptive Bayesian design. We found [evidence for the 
efficacy of x exercises/no evidence for the efficacy of x exercises] with an estimated mean 
effect size of [xx/xx]. This means that… or We recommend that… [recommendation will be 
provided].  
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

Date: 22 March 2022; Swansea University (UK) & Université Grenoble Alpes (France) 
A large, multisite test of self-administered mindfulness 
 
Engaging in mindfulness meditation, in theory, appears simple: One is asked to sit 
and focus one’s attention on the breath and on the present moment, without needing complex 
settings or apparatus. Partly due to this apparent simplicity, mindfulness meditation protocols 
that can be self-administered have increased in accessibility and popularity in recent years 
(Cavanagh et al., 2018).  
Self-administered mindfulness protocols are free or less expensive compared to 
traditional protocols (Spijkerman, Pots, & Bohlmeijer, 2016) and readily available (Cavanagh 
et al. 2014; Wahbeh et al. 2014). These mindfulness interventions can be accessed as self-
help books, or via computer programmes, smartphone apps, or audio and video recordings. 
For example, the last few years witnessed a surge in downloads of mindfulness applications 
such as ‘Calm’, the top English-language meditation app reportedly with 40 million 
downloads (Gebel, 2019), and ‘Headspace’, reportedly with 70 million downloads 
(Headspace, 2021). Features such as the duration or frequency of these interventions are less 
defined, because while the applications might offer modular sessions of varying lengths, the 
onus is on the consumer to decide for how long or how often to engage with it.  
Despite their easy accessibility, the evidence behind these mindfulness interventions 
is debated and some questions remain unanswered, such as: Are these types of intervention 
truly effective in regulating individuals’ stress levels? or Which types of self-administered 
mindfulness exercises, from the plethora of those available, work to downregulate stress? We 
attempted to answer these questions first by conducting a survey aimed at mindfulness 
practitioners in order to know which are the most used or the most popular mindfulness 
exercises. Based on the results of the survey, we then designed a multi-site, highly powered 
study to test the effects and the boundary conditions of four types of self-administered 
mindfulness meditation exercises on stress regulation.  

Date: 22 March 2022; Swansea University (UK) & Université Grenoble Alpes (France) 
Do self-administered mindfulness interventions reduce levels of stress?  
According to Jon Kabat-Zinn (1992, 2003), mindfulness can be defined as “paying 
attention in a particular way: On purpose, in the present moment, and nonjudgmentally”. 
Mindfulness emphasizes attention to the present moment, with awareness of one’s bodily 
sensations or one’s mental content (thoughts, emotions, memories, etc.). Self-administered 
mindfulness interventions share these features, but compared to traditional established 
mindfulness protocols (e.g., mindfulness-based stress reduction - MBSR or mindfulness-
based cognitive therapy - MBCT), do not require the presence of an instructor or and the 
commitment to be in a particular place and time regularly, for 8 weeks, allowing practitioners 
to meditate whenever they choose so (Spijkerman, Pots, & Bohlmeijer, 2016).  
Because self-administered mindfulness interventions hold promises for reducing 
stress levels and are accessible to virtually anyone, it is important to understand whether they 
bring about the expected results. While some studies showed positive results of self-
administered mindfulness interventions on reducing self-reported stress (Cavanagh et al., 
2013; Cavanagh et al., 2018), and a recent meta-analysis pointed in the same direction 
(Taylor et al., 2021), other studies reported less positive outcomes. For instance, Glück and 
Maercker (2011) did not find evidence that a self-guided mindfulness training effectively 
decreased levels of perceived stress and distress for a group of meditators compared to a 
waitlist control group. Finally, a meta-analysis failed to find sufficient evidence regarding the 
efficacy of self-administered mindfulness interventions on stress reduction after applying 
publication bias techniques (Sparacio et al., 2022).  
Which types of self-administered mindfulness exercises work to downregulate stress? 
Another reason why we do not know yet whether self-administered mindfulness 
interventions are efficacious at regulating stress is that self-administered mindfulness include 
a range of different exercises (e.g., body scan, mindful breathing, mindful walking, etc.); 

Date: 22 March 2022; Swansea University (UK) & Université Grenoble Alpes (France) 
current tests evaluate protocols in their entirety, instead of differentiating among these 
exercises. According to Germer et al. (2016), there are a plethora of mindfulness exercises 
that can be divided into three different categories: ‘awareness’, ‘present experience’, and 
‘acceptance’. These different categories are not truly separate, but yet, splitting them into 
three different groups allows us to better understand the potential applied value of certain 
mindfulness exercises that can be self-administered.  
‘Awareness’ mindfulness exercises are typically characterized by a series of steps: 
1) Disengage from an automatic train of thoughts (e.g., pausing a discussion with a friend by 
taking a long breath), 2) focus the attention on an object that is used as an “anchor” (e.g., 
bringing the attention to the breath or to parts of the body), and 3) return the attention to the 
object of focus when one realizes they have been distracted, and then watch where the mind 
wanders next. 
‘Present experience’ mindfulness exercises instruct participants to pay attention 
completely to the activity being carried out (e.g., bringing the attention to the sole of the foot 
while walking). If the mind wanders, the attention is redirected to the present moment and the 
instructions that are given in this set of exercises have the function of fulfilling this objective. 
‘Acceptance’ mindfulness exercises are characterized by applying a non-
judgemental attitude of kindness and curiosity to one’s experience. Practitioners that do these 
types of exercises are invited to cultivate positive feelings towards themselves and to others 
(e.g., directing loving-kindness to themselves or to someone else). 
We currently do not know which category of the exercises described above works 
best for reducing stress levels. Some studies have tested single brief mindfulness exercises 
(Feldman et al., 2010; Hutcherson et al., 2008). To our knowledge, however, none 
investigated the effectiveness of brief stand-alone mindfulness exercises on stress reduction. 
Thus, the aim of our multi-site project is to investigate which self-administered mindfulness 

Date: 22 March 2022; Swansea University (UK) & Université Grenoble Alpes (France) 
exercises were more effective in reducing individuals’ stress levels, compared to three non-
mindful active control conditions randomly sampled.  
Study 1: Survey on self-administered mindfulness 
To identify the most representative mindfulness exercises to use in our multi-site 
project, we conducted a survey to ask mindfulness practitioners for their suggestions 
regarding self-administered mindfulness exercises. that provided a list of the 20 most popular 
meditation techniques. To compile a final list of exercises, we retained the most popular 
exercises suggested by the practitioners taking part in the survey that were also included in 
peer-reviewed literature (Matko et al., 2019). 
Procedure 
We disseminated a Qualtrics survey to mindfulness practitioners (i.e., instructors 
and/or researchers) that we retrieved from lists of subscribers of various mindfulness 
associations and via social media networks (Facebook, Twitter, & LinkedIn) between 
November 17th and December 31th, 2020. Ninety-five mindfulness practitioners took part in 
the survey, of the total 40 completed half of it, and 20 respondents arrived at the end.  
The survey was divided into two parts: The first part asked respondents to suggest 
low-intensity self-administered mindfulness interventions designed to decrease levels of 
stress with a short term efficacy span, or ‘state-level’ stress, while the second part asked them 
to suggest high-intensity self-administered mindfulness interventions that can be aimed at 
changing personality traits that can impact on stress levels (e.g., decreasing ‘trait-level’ 
stress). A low-intensity self-administered mindfulness intervention was defined as a 
“mindfulness intervention that is brief, but long enough to have an impact on stress levels of 
individuals [and] give participants flexibility (to ensure that they do not abandon the study), 
while being effective in reducing stress”. We did not expect this low-intensity intervention to 
substantially impact on traits of participants that predisposes them to higher levels of stress 

Date: 22 March 2022; Swansea University (UK) & Université Grenoble Alpes (France) 
(e.g., trait anxiety, tendency to ruminate). A high-intensity self-administered mindfulness 
intervention was defined as a “mindfulness intervention that is longer, less flexible, but that 
might impact not only on stress levels of participants, but also on personality traits of 
participants that are relevant to the buildup of stress (e.g., trait anxiety, tendency to 
ruminate).”  
We asked the same set of questions for both low- and high-intensity self-administered 
mindfulness interventions, namely: 1) How long the intervention should last, in order to 
observe a significant reduction of participants' stress level (from 1 day to 8 weeks or more), 2) 
How many times a week participants should do exercises of self-administered mindfulness? 
(1 to 7/week), 3) Which type of source they thought would be more effective for delivering 
the intervention (smartphone app, video file, audio file, self-help book, another type of source 
- specify which, or ‘the source is not relevant’), and 4) What types of exercises should be 
included in the intervention (e.g., body scan, focus on breathing, etc.). For each exercise they 
suggested, we asked them 1) If the order of the exercises they listed in the previous question 
was important to achieve stress reduction (yes, maybe, no), and 2) How long they thought it 
should be practiced and how often (length - or daily duration of the exercise in minutes; 
weekly frequency; number of weeks of the intervention).  
Results 
Results of our survey showed that respondents: 1) estimated that smartphone 
applications were the most effective types of self-administered mindfulness exercise for 
reducing stress levels as compared to other cited sources (e.g., books), 2) considered that the 
order of the mindfulness exercises could potentially be relevant to impact levels of stress1 and 
3) assessed that practicing mindfulness daily had the greatest impact on stress reduction. A 
full description of the results is beyond the scope of this manuscript, however a R script with 
 
1 18 respondents answered “maybe” to this question, 14 answered “yes” and 7 answered “no”. 

Date: 22 March 2022; Swansea University (UK) & Université Grenoble Alpes (France) 
the answers of the respondents and a complete report of the survey in PDF can be found on 
the OSF page of the project (https://osf.io/aw2vz/).  
For planning the multi-site study, we relied on practitioners’ answers that included a 
list of exercises to be considered for a low-intensity self-administered mindfulness 
intervention2. The list compiled practitioners’ suggestions and consisted, initially, of 174 
mindfulness exercises (see the list of the exercises document at https://osf.io/br86s/). We then 
removed duplicates and we merged the techniques that we considered to be similar3 (e.g., 
‘mindful walking’ and ‘walk in mindfulness’) or that were spelled differently but referred to 
the same exercise (e.g., ‘body scanning’ and ‘body scan’). We then organized each technique 
according to its dominant element of mindfulness based on Germer’s (2016) system of 
categorization, which included three categories previously mentioned: ‘awareness’, ‘present 
experience’, and ‘acceptance’. Some mindfulness exercises suggested by the practitioners 
were already categorized according to Germer's system (e.g., ‘body scan’ was placed as 
belonging to the category ‘awareness’). For the exercises that were not already categorized, 
the first author made an arbitrary choice based on the similarities between the uncategorized 
exercise and the other exercises already present in that category (e.g., ‘mindful movements’ 
was placed in the category ‘present experience’). 
Finally, for each dominant element, we retained the two exercises that were the most 
cited: Body scan (39 votes) and mindful breathing (37 votes) for ‘awareness’, mindful 
walking (10 votes) and mindful movement (10 votes) for ‘present experience’, and self-
 
2 When we designed the survey, we had not yet outlined the details of the multi-site project, so we asked for 
general information related to self-administered mindfulness protocols. For the purpose of the multi-site project 
we used only a portion of all the information provided by the answers of mindfulness practitioners, however we 
believe that the unused information may help other mindfulness researchers design more rigorous studies on the 
topic. 
3 This process was done by the first author, however it is possible to infer how the simplification was done by 
comparing the files with all exercises (i.e., List of the exercises) and the one where similar exercises were 
merged (i.e., Mindfulness clusters MULTI-SITE; see https://osf.io/br86s/). 

Date: 22 March 2022; Swansea University (UK) & Université Grenoble Alpes (France) 
compassion break (5 votes) and loving kindness meditation (3 votes) for ‘acceptance’ (See 
Mindfulness clusters MULTI-SITE at https://osf.io/br86s/). 
We then cross-referenced our set of self-administered mindfulness exercises with the 
list of 20 popular meditation techniques that Matko et al., (2019) detailed by consulting 637 
meditators with an online survey. By retaining the exercises that were present in both 
approaches we arrived at this final list of self-administered mindfulness exercises: Body scan, 
mindful breathing, mindful walking and loving-kindness meditation. We decided to test these 
four mindfulness exercises in the multi-site project described below. 
Study 2: The multi-site project 
Hypothesis  
We hypothesized that participants allocated to any one of the experimental 
(mindfulness) conditions would experience lower levels of self-reported stress compared to 
participants allocated to an active control conditions4.  
Additionally we explored effects on the dimensions of pleasure, arousal and 
dominance of any of the experimental conditions as compared to the active control 
conditions. Similarly, we also explored the role of neuroticism in reducing levels of stress of 
individuals for the above mentioned conditions. 
Methods 
Materials 
All materials used in the study, including the ethics (IRB) approval documents of all 
the sites involved in the project and the meditations scripts are available on our OSF page 
(https://osf.io/6w2zm/), the analysis code instead can be found on the GitHub repository of 
 
4 Participants who end up in the control group will have an equal chance of listening to an excerpt of one the 
three stories that we selected for the present study. 

Date: 22 March 2022; Swansea University (UK) & Université Grenoble Alpes (France) 
the project (https://github.com/alessandro992/A-large-multi-site-test-of-self-administered-
mindfulness). 
Participants and sites 
Because the guided audio meditations and the active control excerpts recorded for this 
experiment were in English, we limited the study to English native speakers or participants 
who self-assessed their level of English proficiency at the C1/C2 levels from the Common 
European Framework of Reference for Languages (Council of Europe, 2001).  
Participants were excluded if they reported having or having had a history of mental 
illnesses, if they declared having meditated in the previous 6 months, or if they were not 
fluent in English. Each participant was asked to take part in the survey using a smartphone 
with headphones or earphones attached, not a computer or laptop, because one experimental 
condition included mindful walking and, participants being randomly allocated to conditions, 
we needed to ensure that everyone was equally capable to perform any of the mindfulness 
activities. Each site was asked to collect data from at least 70 participants and up to a 
maximum of 130 participants5 in order to be considered for authorship of the article resulting 
from this experiment.  
The data collection will start on March 23th 2022. Sites will be able to begin 
recruiting participants up to three weeks after the actual data collection begins. Sites that fail 
to start data collection up to three weeks from the start of the effective date will be excluded 
from the project. 
Bayesian design analysis 
Prior to the data collection, we simulated data based on a Bayes Factor Design 
Analysis (BFDA; Schönbrodt & Wagenmakers, 2018) to assess the expected efficiency and 
informativeness of the present design. More specifically, the aim of the design analysis was 
 
5 We allowed a maximum of three people, per site, to become part of the authorship team.  

Date: 22 March 2022; Swansea University (UK) & Université Grenoble Alpes (France) 
to establish (1) the expected likelihood of the study to provide compelling relative evidence 
either in favor of H0 (BF01 = 1/10) or H1 (BF10 = 10); (2) the likelihood of obtaining 
convincing but misleading evidence, and (3) the likelihood that the study points into the 
correct direction even if stopped earlier due pragmatic constraints on sample size (Schönbrodt 
& Wagenmakers, 2018).  
Given these aims, we modeled a sequential design with maximum N where the data 
collection continues until either the threshold for compelling evidence is met or the maximum 
N is reached. Initially, forty-one labs indicated interest in the project, we expect to have up to 
30 data-collecting labs. Each lab was expected to collect data of at least N = 70 participants, 
with a stopping N at 120 (translating to Min = 420 and Max = 720 participants per condition). 
We intended to be able to detect an effect size of d = 0.20; here we modeled the true value to 
vary between labs by repeatedly (for each simulation) drawing from a normal distribution, δ 
∼ N(0.20, 0.05), with a 95% probability that the effect size falls between d = 0.10 and 0.30.  
The present study aimed at testing the effectiveness of four stand-alone interventions 
using a between-subjects adaptive group design, where upon hitting a threshold of 
compelling evidence in one condition, the plan was to allocate the rest of the participants into 
other conditions where this has not been the case yet. The design analysis, however, assumed 
a conservative scenario with equal N across all conditions, therefore, simplifying the 
computations to a single between-subjects t-test scenario. 
The results (see Figure 1) show that, given the assumed design, the probability of the 
test to arrive at the boundary of compelling evidence (BF = 10 or 1/10) was .79 (.72 at H1 and 
.07 erroneously at H0). The probability of terminating at maximum N of 720 per condition 
was .21; .05 of showing some evidence for H1 (BF > 3), .13 of being inconclusive (3 > BF > 
1/3), and .03 of showing evidence for H0 (BF < 1/3). For the test of a single condition against 
controls, the sequential design is expected to be 27% more effective than collecting a fixed 

Date: 22 March 2022; Swansea University (UK) & Université Grenoble Alpes (France) 
maximum N per lab, with the average N at stopping point (BF boundary and maximum N) at 
526. Even conservatively assuming a balanced-N situation, the informativeness of the design 
thus appears to be adequate and the use of adaptive design is likely to further enhance 
informativeness and/or resource efficiency. Figure 1 shows the results of the simulation of the 
sequential design with 10000 iterations. 
 
Figure 1. Design analysis for the sequential bayesian design with maximum N 
Procedure 
Participants accessed the experiment via a Qualtrics link. They were provided detailed 
information about the study (see “Participants Information Sheet” included in the IRB 
package, https://osf.io/6w2zm/) and were then asked to provide consent prior to participating. 
Each participant was asked to take part in the survey using a smartphone with headphones or 
earphones attached, not a computer or laptop, because one experimental condition includes 
mindful walking and, participants being randomly allocated to conditions, we needed to 
ensure that everyone would be equally capable to perform the mindfulness activity. To know 
if this condition was verified we included a question in which we asked participants whether 
they started the survey from a device other than a smartphone; if they answered negatively, 

Date: 22 March 2022; Swansea University (UK) & Université Grenoble Alpes (France) 
we asked them to exit the survey and to restart it, this time using a smartphone with 
headphones or earphones attached.  
Participants were also asked to sit in a quiet place such as a room where they could 
not be disturbed for 20 minutes. After providing informed consent, they were asked to 
complete the Neuroticism subscale of the IPIP - 5 NEO Domains (IPIP, 2021) to assess the 
level of neuroticism. Examples of items were “I often feel blue” or “I am filled with doubts 
about things”. Participants could answer a 5-points scale (1 = Very inaccurate, 2 = 
Moderately Inaccurate, 3 = Neither Inaccurate nor Accurate, 4 = Moderately Accurate, 5 = 
Very Accurate). We estimated the scale reliability (i.e., internal consistency) using the omega 
coefficient. Assuming a unitary-factor model, the reliability estimate in the present sample 
was ωu = x. 
After the completion of the neuroticism measure, participants were randomly 
allocated to one of the five conditions6. In each condition, participants were presented with a 
different 15-minutes recording. The four audio files of the mindfulness exercises and the 
three audio files of the stories of the non-mindful active control condition were recorded by a 
certified meditator, to keep the voice constant across conditions. Following a brief description 
of the mindfulness conditions and of the three different stories of the non-mindful active 
control condition. 
Body scan. In body scan, participants were invited to “scan” their parts of the body. 
Every time the mind wandered, participants were invited to bring back the awareness and the 
attention to the part of the body they were “scanning”.  
 
6 Participants in the non-mindful active control condition could listen to the excerpt of one of three stories that 
we selected with an equal chance of getting one story over another. 

Date: 22 March 2022; Swansea University (UK) & Université Grenoble Alpes (France) 
Mindful breathing. During mindful breathing, participants were invited to “stay with 
their breath”, without changing the way they were breathing. When the mind wandered, 
participants were told to bring their attention back to the breath with kindness and patience.  
Loving kindness-meditation. During this practice, participants were encouraged to 
direct loving kindness toward themselves and then to extend these feelings of loving kindness 
towards somebody else. 
Mindful walking. The nature of this condition slightly differed from the rest because 
participants were asked to walk in a quiet place (preferably indoor or in a place as isolated as 
possible from distractions), while listening to the instructions. During this practice, 
participants were invited to bring their awareness to the experience of walking and they were 
invited to “feel” a direct sense of the physical sensations of contact of their feet with the 
ground. 
Non-mindful active control condition. Participants in the control condition had an 
equal probability of listening to an excerpt coming from one of these three books: 
“Silverview” (word count: 1838) by John le Carré (Le Carré's, 2021), “the old man and the 
sea” (word count: 2039) by Ernest Hemingway (Hemingway, 1952) and “Smith of Wootton 
Major” (word count: 2015) by J. R. R. Tolkien (Tolkien, 1967). These three stories were 
chosen because they had a similar word count, they were written in an easy to understand 
English, and did not feature major plot changes so they were unlikely to elicit strong 
emotions. The full transcript of the seven recordings can be found at our OSF project page 
(https://osf.io/6w2zm/). 
 After the 15 minutes of mindfulness exercises or active control listening, participants 
first answered the State-Trait Anxiety Inventory, Form Y (STAI; Spielberger, Gorshu & 
Lushene, 1970). Participants were asked to indicate how they felt in that exact moment on a 
4-points scale (1 = Not at all, 2 = Somewhat, 3 = Moderately so, 4 = Very much so) on 20 

Date: 22 March 2022; Swansea University (UK) & Université Grenoble Alpes (France) 
items (e.g., “I am tense”; “I feel frightened”). For the present study, we only used the part of 
the scale that measures state anxiety as we are interested in self-reported stress of individuals 
with a short-term efficacy span. We calculated the one-factor omega for this scale obtaining a 
reliability estimate of ωu = x.  
Participants then filled in The Self-Assessment Manikin a non-verbal pictorial 
assessment technique that measures three different dimensions: pleasure, arousal, and 
dominance in relation to an object or a stimulus (Bradley & Lang, 1994). Participants were 
invited to observe a series of images and were asked to select the image that best represented 
their emotional state in that exact moment. This scale demonstrated to have high correlation 
with scales measuring the same dimensions (i.e., pleasure, arousal, & dominance; Morris, 
1995).  
Finally, participants answered questions related to their demographic information 
such as age, gender, country of birth, country of residence, and whether they were students or 
not. If participants were students, they were asked to indicate in which university they were 
studying; if participants were not students we inquired about their current job. At the end, 
participants were thanked and debriefed. Based on the site they belong to, participants were 
then redirected to another page to receive credits/payments for completing the study. 
Analysis Plan 
 
 
To assess whether any of the chosen mindfulness exercises were more effective than 
the randomly sampled control conditions to reduce stress in participants, we planned to 
conduct a sequential design. We sampled participants until a Bayes Factor threshold for 
compelling evidence was met or until a maximally feasible number of participants was 
collected (Schönbrodt et al., 2017). Unlike in the frequentist approach, the aim of this 
procedure was not the control of error rates, but to gauge the relative support provided by the 
present data in favor of one of two competing hypotheses, H1 and H0. In the frequentist 

Date: 22 March 2022; Swansea University (UK) & Université Grenoble Alpes (France) 
approach, the practice of adjusting the sampling plan after peeking at the data would have 
increased the Type 1 error rate, but in the Bayesian approach, the data collection could be 
stopped anytime without having any consequences on the interpretation of the Bayes Factor 
(Rouder, 2014). We divided our analysis workflow into confirmatory and exploratory. The 
sequential testing was tied to the confirmatory analysis phase while the exploratory analyses 
had no role in the decisions related to sampling.  
Confirmatory analyses 
As the aim of the present study was to assess the effectiveness of four stand-alone 
mindfulness interventions without any aspirations to draw broad inferences about 
mindfulness intervention in general, we planned to carry out four independent comparisons 
with the active controls. Therefore, we carried out four independent-samples Bayesian t-tests 
to determine whether there was a difference between each mindfulness exercise and the 
active control condition. We employed a two-tailed test using a non-informative JZS Cauchy 
prior for the alternative hypothesis with a default r-scale of √2/2 (Rouder, Speckman, Sun, 
Morey, & Iverson 2009). To account for the hierarchical nature of the data, we compared the 
condition means using a Bayesian mixed-effects model that involved a random intercept for 
lab and for different stories used in the non-mindful active control condition. 
We implemented the sequential design as being adaptive, stopping collecting the data 
for a given test of a condition after obtaining a Bayes Factor of 10 in favor of H1 or a Bayes 
factor of 1/10 in favor of H0., and re-assigning the remaining participants into other 
conditions, where such a threshold has not been met. We chose a Bayes Factor of 10, because 
according to the classification of Lee and Wagenmakers (2013), it demarcates the threshold 
between moderate and strong evidence. We started monitoring the Bayes Factor when there 
were at least 100 participants in each group. We chose 100 arbitrarily, because with a smaller 
sample size, the probability of misleading evidence (i.e., a Bayes Factor trajectory that arrives 

Date: 22 March 2022; Swansea University (UK) & Université Grenoble Alpes (France) 
at the “wrong” boundary, that is, at the H0 boundary when H1 is correct and the other way 
around) would have been higher. Here, using a sample size of 100 and a Bayes Factor of 10 
we aimed to substantially decrease the probability of misleading evidence (Stefan et al., 
2017). 
 We monitored the Bayes Factor and recorded the interim analysis every 3 days to 
check whether the threshold was reached7. If the threshold was not reached (BF of 10 or of 
1/10) we stopped the data collection after that the maximum number of participants8 was 
reached. If for any of the four tests, one of these three conditions was not met (i.e., BF of 10 
in favor of H1; BF of 1/10 in favor of H0; the maximum number of participants is reached), 
the data collection was terminated four months after the start of the experiment. When one of 
these three conditions has been met, we stopped allocating participants to that particular 
experimental condition and we allocated them to the remaining conditions for which this has 
not been the case yet. If the data collection ends before all the sites are able to collect at least 
70 participants9 (because we would have reached a Bayes Factor of 10 in favor of H1 or of 
1/10 in favor of H0 for a given test of a condition), we will continue with the data collection 
by reopening all groups and equitably allocating each participant to each group until each site 
would have collected at least 70 participants. In this case, we would use this sample for 
exploratory analyses. 
Exploratory analyses 
We also carried out analyses exploring the effect of experimental conditions on 
pleasure, arousal, and dominance, and for the potential moderating effect of neuroticism. We 
 
7 Each time we did so, we generated a file in Rmarkdown that we uploaded on the OSF project page. Similarly, 
we generated a Rmarkdown file, twice a week, to document how many participants were collected for each site 
and how many participants were assigned to each experimental group. 
8 The maximum number of participants was set to 120k, where k is the number of sites that took part in the 
study, and 120 was the maximum number of participants that each site committed to collect. 
 
970 is the minimum number of participants that we requested to each site to collect to be considered for 
authorship 

Date: 22 March 2022; Swansea University (UK) & Université Grenoble Alpes (France) 
thus performed three different Bayesian t-tests for each dimension of the Self-Assessment 
Manikin scale (pleasure, arousal and dominance) comparing our experimental conditions 
with the control condition. We then looked at The Bayes Factor to establish whether the data 
favored H1 or H0. Similarly as we did for the confirmatory analyses we compared the 
condition means using a Bayesian mixed-effects model that involved a random intercept for 
lab and for different stories used in the non-mindful active control condition to account for 
the hierarchical nature of the data. 
To check whether neuroticism moderated the effects of the four experimental 
conditions on stress, we compared the model with the interaction to the model with only the 
main effects (using the lmBF function) and we reported the corresponding BF. If the model 
with the interaction was preferred to the model with only the main effects of a BF of 10 or 
more, we would have solid evidence of the moderation of neuroticism on stress. We 
computed the Markov chain Monte Carlo chain (MCMC) to estimate parameters through the 
posterior function, in this way for each condition we were able to assess whether there were 
differences in stress levels for people with high, average, or low neuroticism scores. 
Dealing with careless or insufficient effort responder 
We decided to set a series of rules to deal with careless or insufficient effort 
responders (C/IE; Currant, 2016), to reduce errors and provide more valid results. We 
decided to be conservative in our criteria by excluding participants that were providing too 
unrealistic answers that can hardly be due to casual errors, but at most to a consistent pattern 
in the response modality (i.e., finishing the survey as soon as possible to get 
payments/credits). Some possible issues were limited by some settings we fixed in the 
Qualtrics survey; we forced the answers for the questions connected to our exclusion criteria 

Date: 22 March 2022; Swansea University (UK) & Université Grenoble Alpes (France) 
(meditation experience, english level, mental illnesses) for the questionnaires related to our 
dependent variables/moderator instead the answers were requested10.  
To be sure that participants listened to the 15 minutes mindfulness/control condition 
we blocked the screen with the audio of the meditation/ control condition for 14 minutes (i.e., 
840 seconds) so as not to allow participants to proceed to the following survey page until the 
meditation was actually finished. However, we excluded participants that completed the 
survey in less than 946 seconds, because as in addition to the 15 minutes of the recording we 
added a cut score for response time at 2 seconds an item, by following the recommendations 
of Huang et al., (2012)11 To exclude participants that provided the same response to every 
question (i.e., selecting always the answer “strongly agree”) we performed a long string 
analysis. Here we followed the recommendations of Huang et al., (2012) and we excluded 
from the study individuals with a string of consistent responses equal or greater than 10 (i.e., 
half of the length of the total scale). Furthermore If a participant responded to less than 50% 
of the items on a scale, we excluded that participant's score for that scale. Finally we decided 
not to exclude outliers as we believe that this would have led to the loss of important 
information and we did not perform any transformation of the data.  
Ethics Information, Administrative Organization and Data protection 
The study received ethical approval from Swansea University while the sites that 
participated in the data collection received ethical approval from their local IRBs. To 
minimize the workload to collaborators, we provided an IRB submission pack that sites could 
adapt to their institutions’ requirements. For most sites, only small adjustments to our IRB 
pack were necessary for submission. Each site’s IRB protocols with ethics details and 
acceptance of each protocol can be found on the OSF project page at https://osf.io/6w2zm/. 
 
10If participants do not provide any answer a message appears asking participants whether they want to continue 
to the following part of the survey without answering that particular question.  
11 We had 53 questions resulting in 103 seconds to be added to the 840 seconds of the meditation/control 
condition thus arriving at 946 seconds 

Date: 22 March 2022; Swansea University (UK) & Université Grenoble Alpes (France) 
Swansea University was the administrative organization for the study. Swansea 
University was also the data controller for this project. Personal data of participants were 
processed for the purposes outlined in the information sheet (see the document Information 
Sheet at https://osf.io/xuznc/). Standard ethical procedures involved participants providing 
their consent to participate in this study by completing the consent form that was 
administered at the beginning of the online survey used for the experiment.  
We left each site the possibility to recruit participants in their preferred way. 
Participants could be recruited through the SONA system of the respective institution or via 
crowdsourcing platforms such as mTurk or Prolific academic. Participants could come from 
any geographic area if they met our inclusion criteria and could be given either credits or 
financial compensation in exchange for participation in the study. 
Conflict of interests 
The certified mindfulness instructor that collaborated on the multi-site project only 
recorded the meditations, but was not involved in the writing of any parts of the manuscript 
(e.g., choice of the analyses). 
 
 
 
 
 
 
 
 
 
 

Date: 22 March 2022; Swansea University (UK) & Université Grenoble Alpes (France) 
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