Health Care Workers’ Need for Headspace: Findings From a Multisite Definitive Randomized Controlled Trial of an Unguided Digital Mindfulness-Based Self-help App to Reduce Healthcare Worker Stress

Background Health care workers experience high stress. Accessible, affordable, and effective approaches to reducing stress are lacking. In-person mindfulness-based interventions can reduce health care worker stress but are not widely available or accessible to busy health care workers. Unguided, digital, mindfulness-based self-help (MBSH) interventions show promise and can be flexibly engaged with. However, their effectiveness in reducing health care worker stress has not yet been explored in a definitive trial. Objective This study aimed to investigate the effectiveness of an unguided digital MBSH app (Headspace) in reducing health care worker stress. Methods This was a definitive superiority randomized controlled trial with 2182 National Health Service staff in England recruited on the web and allocated in a 1:1 ratio to fully automated Headspace (n=1095, 50.18%) or active control (Moodzone; n=1087, 49.82%) for 4.5 months. Outcomes were subscales of the Depression, Anxiety, and Stress (primary outcome) Scale short form; Short Warwick Edinburgh Mental Well-being Scale; Maslach Burnout Inventory; 15-item Five-Facet Mindfulness Questionnaire minus Observe items; Self-Compassion Scale–Short Form; Compassionate Love Scale; Penn State Worry Questionnaire; Brooding subscale of the Ruminative Response Scale; and sickness absence. Results Intention-to-treat analyses found that Headspace led to greater reductions in stress over time than Moodzone (b=–0.31, 95% CI –0.47 to –0.14; P<.001), with small effects. Small effects of Headspace versus Moodzone were found for depression (b=–0.24, 95% CI –0.40 to –0.08; P=.003), anxiety (b=–0.19, 95% CI –0.32 to –0.06; P=.004), well-being (b=0.14, 95% CI 0.05-0.23; P=.002), mindfulness (b=0.22, 95% CI 0.09-0.34; P=.001), self-compassion (b=0.48, 95% CI 0.33-0.64; P<.001), compassion for others (b=0.02, 95% CI 0.00-0.04; P=.04), and worry (b=–0.30, 95% CI –0.51 to –0.09; P=.005) but not for burnout (b=–0.19, –0.04, and 0.13, all 95% CIs >0; P=.65, .67, and .35), ruminative brooding (b=–0.06, 95% CI –0.12 to 0.00; P=.06), or sickness absence (γ=0.09, 95% CI –0.18 to 0.34). Per-protocol effects of Headspace (454/1095, 41.46%) versus Moodzone (283/1087, 26.03%) over time were found for stress, self-compassion, and compassion for others but not for the other outcomes. Engagement (practice days per week) and improvements in self-compassion during the initial 1.5-month intervention period mediated pre- to postintervention improvements in stress. Improvements in mindfulness, rumination, and worry did not mediate pre- to postintervention improvements in stress. No serious adverse events were reported. Conclusions An unguided digital MBSH intervention (Headspace) can reduce health care workers’ stress. Effect sizes were small but could have population-level benefits. Unguided digital MBSH interventions can be part of the solution to reducing health care worker stress alongside potentially costlier but potentially more effective in-person mindfulness-based interventions, nonmindfulness courses, and organizational-level interventions. Trial Registration International Standard Randomised Controlled Trial Number ISRCTN15424185; https://tinyurl.com/rv9en5kc

The CONSORT-EHEALTH checklist is intended for authors of randomized trials evaluating web-based and Internet-based applications/interventions, including mobile interventions, electronic games (incl multiplayer games), social media, certain telehealth applications, and other interactive and/or networked electronic applications. Some of the items (e.g. all subitems under item 5 -description of the intervention) may also be applicable for other study designs.
The goal of the CONSORT EHEALTH checklist and guideline is to be a) a guide for reporting for authors of RCTs, b) to form a basis for appraisal of an ehealth trial (in terms of validity) CONSORT-EHEALTH items/subitems are MANDATORY reporting items for studies published in the Journal of Medical Internet Research and other journals / scientific societies endorsing the checklist.
As the CONSORT-EHEALTH checklist is still considered in a formative stage, we would ask that you also RATE ON A SCALE OF 1-5 how important/useful you feel each item is FOR THE PURPOSE OF THE CHECKLIST and reporting guideline (optional).
Mandatory reporting items are marked with a red *. In the textboxes, either copy & paste the relevant sections from your manuscript into this form -please include any quotes from your manuscript in QUOTATION MARKS, or answer directly by providing additional information not in the manuscript, or elaborating on why the item was not relevant for this study. yes: all primary outcomes were significantly better in intervention group vs control partly: SOME primary outcomes were significantly better in intervention group vs control no statistically significant difference between control and intervention potentially harmful: control was significantly better than intervention in one or more outcomes inconclusive: more research is needed Other: not submitted yet -in early draft status not submitted yet -in late draft status, just before submission submitted to a journal but not reviewed yet submitted to a journal and after receiving initial reviewer comments submitted to a journal and accepted, but not published yet Identify the mode of delivery. Preferably use "web-based" and/or "mobile" and/or "electronic game" in the title. Avoid ambiguous terms like "online", "virtual", "interactive". Use "Internet-based" only if Intervention includes non-web-based Internet components (e.g. email), use "computer-based" or "electronic" only if offline products are used. Use "virtual" only in the context of "virtual reality" (3-D worlds). Use "online" only in the context of "online support groups". Complement or substitute product names with broader terms for the class of products (such as "mobile" or "smart phone" instead of "iphone"), especially if the application runs on different platforms. Copy and paste relevant sections from manuscript title (include quotes in quotation marks "like this" to indicate direct quotes from your manuscript), or elaborate on this item by providing additional information not in the ms, or briefly explain why the item is not applicable/relevant for your study The title specifis that the interveniton is "unguided" Copy and paste relevant sections from manuscript title (include quotes in quotation marks "like this" to indicate direct quotes from your manuscript), or elaborate on this item by providing additional information not in the ms, or briefly explain why the item is not applicable/relevant for your study T  R  A  C  T  :  S  t  r  u  c  t  u  r  e  d  s  u  m  m  a  r  y  o  f  t  r  i  a  l  d  e  s  i  g  n  ,  m  e  t  h  o  d  s  ,  r  e  s  u  l  t  s  ,  a  n  d  c  o  n  c  l  u  s  i  o  n  s   N  P  T  e  x  t  e  n  s  i  o  n  :  D  e  s  c  r  i  p  t  i  o  n  o  f  e  x  p  e  r  i  m  e  n  t  a  l  t  r  e  a  t  m  e  n  t  ,  c  o  m  p  a  r  a  t  o  r  ,  c  a  r  e  p  r  o  v  i  d  e  r  s  ,  c  e  n  t  e  r  s  ,  a  n  d  b  l  i  n  d  i  n  g  s  t  a  t  u  s  . subitem not at all important a  t  u  r  e  s  /  f  u  n  c  t  i  o  n  a  l  i  t  i  e  s  /  c  o  m  p  o  n  e  n  t  s  o  f  t  h  e  i  n  t  e  r  v  e  n  t  i  o  n  a  n  d  c  o  m  p  a  r  a  t  o  r  i  n  t  h  e  M  E  T  H  O  D  S  s  e  c  t  i  o  n  o  f  t  h  e  A  B  S  T  R  A  C  T Mention key features/functionalities/components of the intervention and comparator in the abstract. If possible, also mention theories and principles used for designing the site. Keep in mind the needs of systematic reviewers and indexers by including important synonyms. Copy and paste relevant sections from the manuscript abstract (include quotes in quotation marks "like this" to indicate direct quotes from your manuscript), or elaborate on this item by providing additional information not in the ms, or briefly explain why the item is not applicable/relevant for your study "an unguided digital MBSH application (Headspace)" and "fully automated" Copy and paste relevant sections from the manuscript abstract (include quotes in quotation marks "like this" to indicate direct quotes from your manuscript), or elaborate on this item by providing additional information not in the ms, or briefly explain why the item is not applicable/relevant for your study "with 2182 National Health Service (NHS) England staff recruited online, allocated 1:1" Copy and paste relevant sections from the manuscript abstract (include quotes in quotation marks "like this" to indicate direct quotes from your manuscript), or elaborate on this item by providing additional information not in the ms, or briefly explain why the item is not applicable/relevant for your study "Headspace (n=1095) or an active-control (Moodzone, n=1087)" and "Per protocol effects of Headspace (n=454) versus Moodzone (n=283)" Conclusions/Discussions in abstract for negative trials: Discuss the primary outcome -if the trial is negative (primary outcome not changed), and the intervention was not used, discuss whether negative results are attributable to lack of uptake and discuss reasons.  and "The present study sought to overcome some of the methodological limitations of previous related research and extend our understanding of the potential effects of unguided MBSH among healthcare workers. The aim of this large multi-site randomised controlled trial (RCT) is to explore the effectiveness of unguided digital MBSH in comparison to an active-control condition (note that comparisons to active controls are lacking in RCTs of MBIs; [30]) for healthcare workers in targeting stress (primary outcome), mental health outcomes (depression, anxiety, and wellbeing), work-related outcomes (work-related burnout, sickness absence and compassion-for-others) and proposed mechanisms of action (intervention engagement, rumination, worry, mindfulness and self-compassion). To explore its potential as a healthcare-wide intervention to reduce healthcare worker stress, the trial recruited across the full range of NHS organisation types (GP/primary care, hospital trusts, community trusts, mental health/learning disability trusts and ambulance trusts), across geographically and socio-demographically diverse regions of England and across a range of NHS job roles (medical, nursing, allied health professions, psychological and the wider healthcare support roles)." Your response is too large. Try shortening some answers. Copy and paste relevant sections from the manuscript (include quotes in quotation marks "like this" to indicate direct quotes from your manuscript), or elaborate on this item by providing additional information not in the ms, or briefly explain why the item is not applicable/relevant for your study "The present study sought to overcome some of the methodological limitations of previous related research and extend our understanding of the potential effects of unguided MBSH among healthcare workers. The aim of this large multi-site randomised controlled trial (RCT) is to explore the effectiveness of unguided digital MBSH in comparison to an active-control condition (note that comparisons to active controls are lacking in RCTs of MBIs; [30]) for healthcare workers in targeting stress (primary outcome), mental health outcomes (depression, anxiety, and wellbeing), work-related outcomes (work-related burnout, sickness absence and compassion-for-others) and proposed mechanisms of action (intervention engagement, rumination, worry, mindfulness and self-compassion). To explore its potential as a healthcare-wide intervention to reduce healthcare worker stress, the trial recruited across the full range of NHS organisation types (GP/primary care, hospital trusts, community trusts, mental health/learning disability trusts and ambulance trusts), across geographically and socio-demographically diverse regions of England and across a range of NHS job roles (medical, nursing, allied health professions, psychological and the wider healthcare support roles)." and "The primary hypothesis is that participants allocated to unguided digital MBSH will show greater reductions in stress from baseline to post-intervention (4.5 months following randomisation) in comparison to participants in the active control trial arm. Secondary hypotheses are that unguided digital MBSH will be more effective than the active-control at improving mental health outcomes, work-related outcomes and potential mechanisms of action from baseline to after the initial intervention period (1.5 months post randomisation) and from baseline to post-intervention Analyses examining whether intervention engagement and improvements in mindfulness, self-compassion, worry and rumination mediate the effects of intervention on improvements in stress were planned to ascertain intervention-specific mechanisms of action." Your response is too large. Try shortening some answers. Copy and paste relevant sections from the manuscript (include quotes in quotation marks "like this" to indicate direct quotes from your manuscript), or elaborate on this item by providing additional information not in the ms, or briefly explain why the item is not applicable/relevant for your study "As Headspace is a 'live' product, the programme structure was non-static and participants were able to access newly released and/or changing content as it became available." and "As with Headspace, a 'live' non-static version of Moodzone was utilised in the study, meaning that participants could access new and/or changing content as it became available" Copy and paste relevant sections from the manuscript (include quotes in quotation marks "like this" to indicate direct quotes from your manuscript), or elaborate on this item by providing additional information not in the ms, or briefly explain why the item is not applicable/relevant for your study "Participants had to: i) be employed within an NHS trust or GP practice in England; ii) be working in roles that involved direct contact with patients for a minimum of one-day per week; iii) be currently in work (i.e. not on long-term sickness absence); iv) be willing to refrain from engaging in other psychological interventions during the course of the study; v) have regular personal access to an Apple/Android smartphone/tablet or a computer with internet access; vi) be aged 18 years or over; and vii) have sufficient English language skills to read and understand the intervention materials. There were no additional exclusion criteria." Your response is too large. Try shortening some answers. Copy and paste relevant sections from the manuscript (include quotes in quotation marks "like this" to indicate direct quotes from your manuscript), or elaborate on this item by providing additional information not in the ms, or briefly explain why the item is not applicable/relevant for your study participants should "have regular personal access to an Apple/Android smartphone/tablet or a computer with internet access" a c e a s s e s s m e n t s : Open vs. closed, web-based vs. face-to-face assessments: Mention how participants were recruited (online vs. offline), e.g., from an open access website or from a clinic, and clarify if this was a purely webbased trial, or there were face-to-face components (as part of the intervention or for assessment), i.e., to what degree got the study team to know the participant. In online-only trials, clarify if participants were quasi-anonymous and whether having multiple identities was possible or whether technical or logistical measures (e.g., cookies, email confirmation, phone calls) were used to detect/prevent these. Copy and paste relevant sections from the manuscript (include quotes in quotation marks "like this" to indicate direct quotes from your manuscript), or elaborate on this item by providing additional information not in the ms, or briefly explain why the item is not applicable/relevant for your study "NHS staff were recruited via posters and leaflets in NHS settings, invitation emails sent through NHS organisations and study advertisements on staff webpages and/or newsletters. Potential participants were directed to the study website hosted by Qualtrics XM [57] where they could read the participant information and confirm eligibility and informed consent. After consenting, participants were emailed a web-link along with a unique ID code and asked to complete the T1 measures on Qualtrics. Participants completed T1 measures and were allocated automatically to Headspace or Moodzone, using 1:1 block randomisation with a block size of 4 by Qualtrics. To ensure allocation concealment, members of the research team responsible for collecting data and communicating with participants were blind to block size." and "As all assessments were completed online without researchers present, the potential for researcher bias to influence assessment outcomes was minimised." Information given during recruitment. Specify how participants were briefed for recruitment and in the informed consent procedures (e.g., publish the informed consent documentation as appendix, see also item X26), as this information may have an effect on user self-selection, user expectation and may also bias results. Copy and paste relevant sections from the manuscript (include quotes in quotation marks "like this" to indicate direct quotes from your manuscript), or elaborate on this item by providing additional information not in the ms, or briefly explain why the item is not applicable/relevant for your study "where they could read the participant information and confirm eligibility and informed consent (see Appendix 2)." Your response is too large. Try shortening some answers. Copy and paste relevant sections from the manuscript (include quotes in quotation marks "like this" to indicate direct quotes from your manuscript), or elaborate on this item by providing additional information not in the ms, or briefly explain why the item is not applicable/relevant for your study "As all assessments were completed online without researchers present, the potential for researcher bias to influence assessment outcomes was minimised." Clearly report if outcomes were (self-)assessed through online questionnaires (as common in web-based trials) or otherwise. Copy and paste relevant sections from the manuscript (include quotes in quotation marks "like this" to indicate direct quotes from your manuscript), or elaborate on this item by providing additional information not in the ms, or briefly explain why the item is not applicable/relevant for your study "participants were emailed a web-link along with a unique ID code and asked to selfcomplete the T1 measures on Qualtrics" and "At 35-days post-randomisation participants were emailed a link to complete T2 assessments on Qualtrics" and "At 125-days postrandomisation, participants were emailed a link to complete the T3 assessment on Qualtrics" Your response is too large. Try shortening some answers.  Copy and paste relevant sections from the manuscript (include quotes in quotation marks "like this" to indicate direct quotes from your manuscript), or elaborate on this item by providing additional information not in the ms, or briefly explain why the item is not applicable/relevant for your study The participant information sheet informed participants that the study was sponsored by the University of Sussex. Copy and paste relevant sections from the manuscript (include quotes in quotation marks "like this" to indicate direct quotes from your manuscript), or elaborate on this item by providing additional information not in the ms, or briefly explain why the item is not applicable/relevant for your study Your response is too large. Try shortening some answers.

"Headspace
The Headspace MBSH digital programme [38] offers a range of brief mindfulness-based practices alongside psychoeducational material. The Headspace MBSH digital programme can be accessed via a website [43] or app available on the Apple app store or the Android Play store. Headspace offers a range of mindfulness-based practices and psychoeducational animations, including introductory series that consist of daily sessions designed to teach foundational mindfulness principles and practices, as well as packs designed for more specific emotional difficulties (e.g. stress, anxiety) and brief 'SOS' mindfulness practices, designed to be used in times of acute stress. Headspace also offers guidance on informal mindfulness practices that can be undertaken while carrying out everyday activities, such as running and cycling and there is written information, including research evidence relating to mindfulness and an FAQ section. At the time of the study mindfulness practices were verbally guided by Andy Puddicombe; a founder of Headspace with many years' experience of mindfulness practice. For the introductory sessions, users are verbally guided to bring non-judgemental awareness to the body, breath, thoughts and feelings, with later sessions also inviting users to bring awareness to difficulties arising during practice (e.g. boredom, restlessness) and behavioural choices. At the time of recruitment, users were invited to start the Headspace programme by completing the 'Take Ten' introductory pack, which involved undertaking guided ten-minute mindfulness practices daily for ten consecutive days. On completion of 'Take Ten', participants were provided with unlimited access to the full range of Headspace content. While participants were free to choose which content they engaged with, they were invited to carry out at least one tenminute mindfulness practice daily for the duration of the study. While practices range in length from three to 20-minutes, users can select the duration of most sessions. As Headspace is a 'live' product, the programme structure was non-static and participants were able to access newly released and/or changing content as it became available.

Moodzone
The NHS Moodzone psychoeducational digital platform [41] was utilised as an active control. At the time of recruitment, the website offered a range of evidence-based psychosocial recommendations, advice and guidance on how to effectively manage workrelated stress and mental health difficulties. The initial webpage was divided into the following sections: 'What causes work stress?', 'How to manage work stress', 'Learn to speak out', 'Spot the signs of work stress', and 'Who else can help with work stress?'; each providing information and/ or recommendations or guidance relevant to the respective question. Moodzone also included information, videos and audio-tracks/podcasts and links to other related resources. Participants were invited to engage with the Moodzone website for 10-minutes a day for the duration of the study. Copy and paste relevant sections from the manuscript (include quotes in quotation marks "like this" to indicate direct quotes from your manuscript), or elaborate on this item by providing additional information not in the ms, or briefly explain why the item is not applicable/relevant for your study Both interventions were developed prior to the study and independently of the research team.

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Revisions and updating. Clearly mention the date and/or version number of the application/intervention (and comparator, if applicable) evaluated, or describe whether the intervention underwent major changes during the evaluation process, or whether the development and/or content was "frozen" during the trial. Describe dynamic components such as news feeds or changing content which may have an impact on the replicability of the intervention (for unexpected events see item 3b). Copy and paste relevant sections from the manuscript (include quotes in quotation marks "like this" to indicate direct quotes from your manuscript), or elaborate on this item by providing additional information not in the ms, or briefly explain why the item is not applicable/relevant for your study "As Headspace is a 'live' product, the programme structure was non-static and participants were able to access newly released and/or changing content as it became available." "As with Headspace, a 'live' non-static version of Moodzone was utilised in the study, meaning that participants could access new and/or changing content as it became available." "It should be noted that while very similar content is still available [44] , the Moodzone website utilised in the study is no longer active." Copy and paste relevant sections from the manuscript (include quotes in quotation marks "like this" to indicate direct quotes from your manuscript), or elaborate on this item by providing additional information not in the ms, or briefly explain why the item is not applicable/relevant for your study Neither of the interventions were owned by the research team and no members of the research team had access to the intervention source code.

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Digital preservation: Provide the URL of the application, but as the intervention is likely to change or disappear over the course of the years; also make sure the intervention is archived (Internet Archive, webcitation.org, and/or publishing the source code or screenshots/videos alongside the article). As pages behind login screens cannot be archived, consider creating demo pages which are accessible without login. Copy and paste relevant sections from the manuscript (include quotes in quotation marks "like this" to indicate direct quotes from your manuscript), or elaborate on this item by providing additional information not in the ms, or briefly explain why the item is not applicable/relevant for your study ""Following completion of the T1 assessment, participants were emailed information on how to access their allocated intervention." and "Intervention participants were given 12 months free access to Headspace and Moodzone was available free-of-charge." Your response is too large. Try shortening some answers.  [43] or app available on the Apple app store or the Android Play store. Headspace offers a range of mindfulness-based practices and psychoeducational animations, including introductory series that consist of daily sessions designed to teach foundational mindfulness principles and practices, as well as packs designed for more specific emotional difficulties (e.g. stress, anxiety) and brief 'SOS' mindfulness practices, designed to be used in times of acute stress. Headspace also offers guidance on informal mindfulness practices that can be undertaken while carrying out everyday activities, such as running and cycling and there is written information, including research evidence relating to mindfulness and an FAQ section. At the time of the study mindfulness practices were verbally guided by Andy Puddicombe; a founder of Headspace with many years' experience of mindfulness practice. For the introductory sessions, users are verbally guided to bring non-judgemental awareness to the body, breath, thoughts and feelings, with later sessions also inviting users to bring awareness to difficulties arising during practice (e.g. boredom, restlessness) and behavioural choices. At the time of recruitment, users were invited to start the Headspace programme by completing the 'Take Ten' introductory pack, which involved undertaking guided ten-minute mindfulness practices daily for ten consecutive days. On completion of 'Take Ten', participants were provided with unlimited access to the full range of Headspace content. While participants were free to choose which content they engaged with, they were invited to carry out at least one tenminute mindfulness practice daily for the duration of the study. While practices range in length from three to 20-minutes, users can select the duration of most sessions. As Headspace is a 'live' product, the programme structure was non-static and participants were able to access newly released and/or changing content as it became available.

Moodzone
The NHS Moodzone psychoeducational digital platform [41] was utilised as an active control. At the time of recruitment, the website offered a range of evidence-based psychosocial recommendations, advice and guidance on how to effectively manage workrelated stress and mental health difficulties. The initial webpage was divided into the following sections: 'What causes work stress?', 'How to manage work stress', 'Learn to speak out', 'Spot the signs of work stress', and 'Who else can help with work stress?'; each providing information and/ or recommendations or guidance relevant to the respective question. Moodzone also included information, videos and audio-tracks/podcasts and links to other related resources. Participants were invited to engage with the Moodzone website for 10-minutes a day for the duration of the study. It should be noted that while very similar content is still available [44] , the Moodzone website utilised in the study is no longer active. As with Headspace, a 'live' non-static version of Moodzone was utilised in the study, meaning that participants could access new and/or changing content as it became available. Prior to the present study, adequately powered trials of Moodzone had not been undertaken. However, related evidence from a meta-analysis of RCTs identified a significant small effect (d = .20, Pp = .04) of passive psychoeducational interventions compared to control conditions in reducing depression and psychological distress at post-intervention [45]." Your response is too large. Try shortening some answers. Copy and paste relevant sections from the manuscript (include quotes in quotation marks "like this" to indicate direct quotes from your manuscript), or elaborate on this item by providing additional information not in the ms, or briefly explain why the item is not applicable/relevant for your study "participants were invited to engage with their allocated intervention for ten-minutes per day, every day, for the initial 30-day study period. At 35-days post-randomisation participants were emailed a link to complete T2 assessment on Qualtrics and invited to continue engaging with their allocated intervention for ten-minutes per day for the remaining 90-day study period." Clarify the level of human involvement (care providers or health professionals, also technical assistance) in the e-intervention or as co-intervention (detail number and expertise of professionals involved, if any, as well as "type of assistance offered, the timing and frequency of the support, how it is initiated, and the medium by which the assistance is delivered". It may be necessary to distinguish between the level of human involvement required for the trial, and the level of human involvement required for a routine application outside of a RCT setting (discuss under item 21 -generalizability).
C l e a r s e l e c t i o n Your response is too large. Try shortening some answers. Copy and paste relevant sections from the manuscript (include quotes in quotation marks "like this" to indicate direct quotes from your manuscript), or elaborate on this item by providing additional information not in the ms, or briefly explain why the item is not applicable/relevant for your study For the intervneiton: "The research team were available to answer technical questions/ queries via email. No further support was provided." For study assessments: "Participants who did not complete assessments within one week of them being sent were reminded to do so via email. One reminder email was sent to complete T1 assessments and a maximum of four reminder emails at weekly intervals were sent for T2 and T3 assessments." Your response is too large. Try shortening some answers. Sickness absence measured at T1 and T3 was assessed using one-item that asked participants to report how many days they had been absent from work due to sickness during the previous three months. • Demographic information assessed at T1 including participants' age, gender, marital status, number of children under 18 years, number of children aged 18 years or over, NHS job role, trust and team, number of hours worked per week in said NHS job role, highest level of education, individual and household annual incomes, ethnicity, and perceived relative socio-economic status (SES), with response options from 1 (lowest) to 10 (highest) perceived SES [53].
• Intervention expectancy at T1 (Credibility/Expectancy Questionnaire, CEQ; [54]) • Self-reported intervention engagement at T2 and T3: (1) formal engagement: selfreported average number of days/week spent following a guided mindfulness meditation on Headspace/following a recommended stress-management/wellbeing strategy on the Moodzone webpage; and (2) informal engagement: self-reported average number of days/week they brought mindfulness to a daily activity or brought the recommended stressmanagement/wellbeing strategies from Moodzone into their daily life. At T2, these questions were asked in relation to the previous month and at T3 they were asked in relation to the previous three months. • Intervention evaluations at T2 and T3: Participants were asked how likely they were to recommend the intervention to friends and family; how much they really felt that their allocated intervention had helped their wellbeing; and how likely they were to continue practicing mindfulness (Headspace participants) or stress management/wellbeing strategies (Moodzone participants) over the following six-months.
• Hypothesis guess at T3: Participants were asked to state what they thought the purpose of the study was. • Intervention deviations at T3: Participants were asked to indicate whether or not they had engaged with the alternative study intervention during the course of the study. • Prior mindfulness experience at T3: Participants were asked to indicate their experiences of mindfulness prior to the study, including MBCT/MBSR, MBSH, Headspace, and how often they had practiced mindfulness. Participants were also asked to indicate the extent to which they agreed/disagreed that they had experienced "lasting bad effects" from using their allocated intervention (based on Crawford et al [56]). If participants agreed or strongly agreed, they were asked to provide further details." Your response is too large. Try shortening some answers. Copy and paste relevant sections from the manuscript (include quotes in quotation marks "like this" to indicate direct quotes from your manuscript), or elaborate on this item by providing additional information not in the ms, or briefly explain why the item is not applicable/relevant for your study "To ensure allocation concealment, members of the research team responsible for collecting data and communicating with participants were blind to block size." and "To improve trial quality and blind participants to study condition and direction of study hypotheses, advertisements about the study simply referred to both conditions as "online interventions to reduce NHS staff stress" and details of the alternative/non-allocated intervention was not communicated to participants until T3 assessments (after outcome and engagement measures had been taken). As all assessments were completed online without researchers present, the potential for researcher bias to influence assessment outcomes was minimised. All but the mediation analysis was conducted blind to study arm." Informed consent procedures (4a-ii) can create biases and certain expectations -discuss e.g., whether participants knew which intervention was the "intervention of interest" and which one was the "comparator". Copy and paste relevant sections from the manuscript (include quotes in quotation marks "like this" to indicate direct quotes from your manuscript), or elaborate on this item by providing additional information not in the ms, or briefly explain why the item is not applicable/relevant for your study "To improve trial quality and blind participants to study condition and direction of study hypotheses, advertisements about the study simply referred to both conditions as "online interventions to reduce NHS staff stress" and details of the alternative/non-allocated intervention was not communicated to participants until T3 assessments (after outcome and engagement measures had been taken)." Copy and paste relevant sections from the manuscript (include quotes in quotation marks "like this" to indicate direct quotes from your manuscript), or elaborate on this item by providing additional information not in the ms, or briefly explain why the item is not applicable/relevant for your study The active control intervnention was described as follows: "Moodzone The NHS Moodzone psychoeducational digital platform [41] was utilised as an active control. At the time of recruitment, the website offered a range of evidence-based psychosocial recommendations, advice and guidance on how to effectively manage workrelated stress and mental health difficulties. The initial webpage was divided into the following sections: 'What causes work stress?', 'How to manage work stress', 'Learn to speak out', 'Spot the signs of work stress', and 'Who else can help with work stress?'; each providing information and/ or recommendations or guidance relevant to the respective question. Moodzone also included information, videos and audio-tracks/podcasts and links to other related resources. Participants were invited to engage with the Moodzone website for 10-minutes a day for the duration of the study. It should be noted that while very similar content is still available [44] , the Moodzone website utilised in the study is no longer active. As with Headspace, a 'live' non-static version of Moodzone was utilised in the study, meaning that participants could access new and/or changing content as it became available. Prior to the present study, adequately powered trials of Moodzone had not been undertaken. However, related evidence from a meta-analysis of RCTs identified a significant small effect (d = .20, Pp = .04) of passive psychoeducational interventions compared to control conditions in reducing depression and psychological distress at post-intervention [45]." Your response is too large. Try shortening some answers.  N  P  T  :  W  h  e  n  a  p  p  l  i  c  a  b  l  e  ,  d  e  t  a  i  l  s  o  f  w  h  e  t  h  e  r  a  n  d  h  o  w  t  h  e  c  l  u  s  t  e  r  i  n  g  b  y  c  a  r  e  p  r  o  v  i  d  e  r  s  o  r  c  e  n  t  e  r  s  w  a  s  a  d  d  r  e  s  s  e  d Your response is too large. Try shortening some answers. Copy and paste relevant sections from the manuscript (include quotes in quotation marks "like this" to indicate direct quotes from your manuscript), or elaborate on this item by providing additional information not in the ms, or briefly explain why the item is not applicable/relevant for your study The information from the manuscript is too large for this section so please see the manuscript for full details "Data Analysis Plan

Handling Missing Data
There were a minimal number of items missing at the item level and missing values for missing items were imputed (using a single imputation) using predictive mean matching in mice [65]. At the scale level, multiple imputation was used to handle missing values. Further details are given in Supplementary Material 2.

Model Selection
Because participants were nested within job roles (Level 3), there are good reasons to model variation in intervention effects between job roles [66]. In such a model there is participant-level randomization to intervention arms and job role acts as a crossed effect. We can think of time (i) as being nested within participants (j), nested within job roles (k), but the effect of treatment arm occurs at level 2 (the participant level), not Level 3 (the job role level), of the hierarchy. This situation is described by the following model: Level 1: This saturated model includes random effects for time, trial arm and their interaction at Level 3. However, this model resulted in convergence problems that yielded erratic estimates of the random effects involving trial arm in the raw sample and nearly all imputed samples. Based on this pre-analysis, a simpler model seemed more appropriate in which only time was treated as a random effect and only at Level 2. However, to model Level 3 variability in outcomes, a random intercept (at Level 3) was included. This simpler model converged in all imputed samples. The resulting model can be described as follows (notice at level 3 two random effects have been knocked out): Level 1: To sum up, hypotheses were tested using a growth model fit as a general linear mixed model (GLMM) with observations (Level 1) nested within participants (Level 2) nested within job roles (Level 3). Time (time from baseline that responses were recorded) and trial arm are predictors. The effect of the intervention was quantified and tested with the interaction between time and trial arm, which shows the degree to which the change in the outcome over time is different in the two trial arms. Between-group effects were reported separately at T2 and T3 in the event of significant (Pp < .05) trial arm x time interactions. The primary analysis was conducted on the ITT sample with the multiply imputed data sets. Secondary analysis was conducted on the per protocol sample (formal engagement T1-T2 on at least 3 days/week; [67]) with the multiply imputed data sets." Your response is too large. Try shortening some answers. Imputation techniques to deal with attrition / missing values: Not all participants will use the intervention/comparator as intended and attrition is typically high in ehealth trials. Specify how participants who did not use the application or dropped out from the trial were treated in the statistical analysis (a complete case analysis is strongly discouraged, and simple imputation techniques such as LOCF may also be problematic [4] Copy and paste relevant sections from the manuscript (include quotes in quotation marks "like this" to indicate direct quotes from your manuscript), or elaborate on this item by providing additional information not in the ms, or briefly explain why the item is not applicable/relevant for your study ""Ethical approval (Reference: ER/HT207/8) was provided by the University of Sussex and study approval was granted by the Health Research Authority (Reference: 16/HRA/5525)." Copy and paste relevant sections from the manuscript (include quotes in quotation marks "like this" to indicate direct quotes from your manuscript), or elaborate on this item by providing additional information not in the ms, or briefly explain why the item is not applicable/relevant for your study "Potential participants were directed to the study website hosted by Qualtrics XM [57] where they could read the participant information and confirm eligibility and informed consent. " Copy and paste relevant sections from the manuscript (include quotes in quotation marks "like this" to indicate direct quotes from your manuscript), or elaborate on this item by providing additional information not in the ms, or briefly explain why the item is not applicable/relevant for your study Details of who participants can contact if distress are shown in the Participant Information Sheet (Appendix 2).
Your response is too large. Try shortening some answers. Copy and paste relevant sections from the manuscript or cite the figure number if applicable (include quotes in quotation marks "like this" to indicate direct quotes from your manuscript), or elaborate on this item by providing additional information not in the ms, or briefly explain why the item is not applicable/relevant for your study This is not included in the current study.
Your response is too large. Try shortening some answers. Copy and paste relevant sections from the manuscript (include quotes in quotation marks "like this" to indicate direct quotes from your manuscript), or elaborate on this item by providing additional information not in the ms, or briefly explain why the item is not applicable/relevant for your study This is not revelant to the study.
Your response is too large. Try shortening some answers. Report multiple "denominators" and provide definitions: Report N's (and effect sizes) "across a range of study participation [and use] thresholds" [1], e.g., N exposed, N consented, N used more than x times, N used more than y weeks, N participants "used" the intervention/comparator at specific pre-defined time points of interest (in absolute and relative numbers per group). Always clearly define "use" of the intervention. Copy and paste relevant sections from the manuscript (include quotes in quotation marks "like this" to indicate direct quotes from your manuscript), or elaborate on this item by providing additional information not in the ms, or briefly explain why the item is not applicable/relevant for your study The primary analysis is defined as intention to treat : "Primary Outcome (Stress) Intention to Treat Analysis In addition to primary/secondary (clinical) outcomes, the presentation of process outcomes such as metrics of use and intensity of use (dose, exposure) and their operational definitions is critical. This does not only refer to metrics of attrition (13-b) (often a binary variable), but also to more continuous exposure metrics such as "average session length". These must be accompanied by a technical description how a metric like a "session" is defined (e.g., timeout after idle time) [1] (report under item 6a Copy and paste relevant sections from the manuscript (include quotes in quotation marks "like this" to indicate direct quotes from your manuscript), or elaborate on this item by providing additional information not in the ms, or briefly explain why the item is not applicable/relevant for your study This information was not recorded in the current study.
Your response is too large. Try shortening some answers.
D I  S  C  U  S  S  I  O  N   2  2  )  I  n  t  e  r  p  r  e  t  a  t  i  o  n  c  o  n  s  i  s  t  e  n  t  w  i  t  h  r  e  s  u  l  t  s  ,  b  a  l  a  n  c  i  n  g  b  e  n  e  f  i  t  s  a  n  d  h  a  r  m  s  ,  a  n  d  c  o  n  s  i  d  e  r  i  n  g  o  t  h  e  r  r  e  l  e  v  a  n  t  e  v  i  d  e  n  c  e   N  P  T  :  I  n  a  d  d  i  t  i  Copy and paste relevant sections from the manuscript (include quotes in quotation marks "like this" to indicate direct quotes from your manuscript), or elaborate on this item by providing additional information not in the ms, or briefly explain why the item is not applicable/relevant for your study A range of limitations are specified in the Discussion.
Your response is too large. Try shortening some answers. Copy and paste relevant sections from the manuscript (include quotes in quotation marks "like this" to indicate direct quotes from your manuscript), or elaborate on this item by providing additional information not in the ms, or briefly explain why the item is not applicable/relevant for your study Routine implementation of Headspace and how this might differ in routine pratice are explored in the Discussion.
Your response is too large. Try shortening some answers. Copy and paste relevant sections from the manuscript (include quotes in quotation marks "like this" to indicate direct quotes from your manuscript), or elaborate on this item by providing additional information not in the ms, or briefly explain why the item is not applicable/relevant for your study ""Funding: This study was supported by a PhD studentship awarded to the first author jointly funded by Headspace and by the ESRC (ES/J500173/1). Data analysis and writing of the manuscript were conducted independently from Headspace and Headspace did not have any influence over the decision to publish findings." Copy and paste relevant sections from the manuscript (include quotes in quotation marks "like this" to indicate direct quotes from your manuscript), or elaborate on this item by providing additional information not in the ms, or briefly explain why the item is not applicable/relevant for your study ""Declaration of Interests: The first author was awarded a PhD studentship for this work by Headspace. The second author has received research and consultancy funding from digital healthcare companies including Headspace. The third author declares no conflicts of interest. The last author is Research Lead for [institution name removed to preserve anonymity] and has received research funding, including from NIHR and Headspace, to evaluate mindfulness-based interventions" Your response is too large. Try shortening some answers. It would be helpful to be able to save reponses when in progress to avoid potentially losing responses (e.g. if network connection drops). Also, the form requires pasting from the manuscript but about half way through a warning came up saying the length was exceeded so that pasting from the manuscript was no longer possible. Otherwise though this was a helpful process.

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