Efficacy of an Unguided, Digital Single-Session Intervention for Internalizing Symptoms in Web-Based Workers: Randomized Controlled Trial

Background The Common Elements Toolbox (COMET) is an unguided digital single-session intervention (SSI) based on principles of cognitive behavioral therapy and positive psychology. Although unguided digital SSIs have shown promise in the treatment of youth psychopathology, the data are more mixed regarding their efficacy in adults. Objective This study aimed to investigate the efficacy of COMET-SSI versus a waiting list control in depression and other transdiagnostic mental health outcomes for Prolific participants with a history of psychopathology. Methods We conducted an investigator-blinded, preregistered randomized controlled trial comparing COMET-SSI (n=409) with an 8-week waiting list control (n=419). Participants were recruited from the web-based workspace Prolific and assessed for depression, anxiety, work and social functioning, psychological well-being, and emotion regulation at baseline and at 2, 4, and 8 weeks after the intervention. The main outcomes were short-term (2 weeks) and long-term (8 weeks) changes in depression and anxiety. The secondary outcomes were the 8-week changes in work and social functioning, well-being, and emotion regulation. Analyses were conducted according to the intent-to-treat principle with imputation, without imputation, and using a per-protocol sample. In addition, we conducted sensitivity analyses to identify inattentive responders. Results The sample comprised 61.9% (513/828) of women, with a mean age of 35.75 (SD 11.93) years. Most participants (732/828, 88.3%) met the criteria for screening for depression or anxiety using at least one validated screening scale. A review of the text data suggested that adherence to the COMET-SSI was near perfect, there were very few inattentive respondents, and satisfaction with the intervention was high. However, despite being powered to detect small effects, there were negligible differences between the conditions in the various outcomes at the various time points, even when focusing on subsets of individuals with more severe symptoms. Conclusions Our results do not support the use of the COMET-SSI in adult Prolific participants. Future work should explore alternate ways of intervening with paid web-based participants, including matching individuals to SSIs they may be most responsive to. Trial Registration ClinicalTrials.gov NCT05379881, https://clinicaltrials.gov/ct2/show/NCT05379881

Is this a full powered effectiveness trial or a pilot/feasibility trial? * Manuscript tracking number * If this is a JMIR submission, please provide the manuscript tracking number under "other" (The ms tracking number can be found in the submission acknowledgement email, or when you login as author in JMIR. If the paper is already published in JMIR, then the ms tracking number is the four-digit number at the end of the DOI, to be found at the bottom of each published article in JMIR) TITLE AND ABSTRACT 1a) TITLE: Identification as a randomized trial in the title

1a-i) Identify the mode of delivery in the title
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 o ine 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. Does your paper address subitem 1a-i? * 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 brie y explain why the item is not applicable/relevant for your study "Efficacy of an unguided web-based single session intervention for depression in online workers: Randomized controlled trial"

1a-ii) Non-web-based components or important co-interventions in title
Mention non-web-based components or important co-interventions in title, if any (e.g., "with telephone support").
C l e a r s e l e c t i o n Does your paper address subitem 1a-ii?
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 brie y explain why the item is not applicable/relevant for your study No. The intervention has no components that are not web-based so this is not included in the title subitem not at all important 1 2 3 4 5 essential 1b) ABSTRACT: Structured summary of trial design, methods, results, and conclusions NPT extension: Description of experimental treatment, comparator, care providers, centers, and blinding status.
1a-iii) Primary condition or target group in the title Mention primary condition or target group in the title, if any (e.g., "for children with Type I Diabetes") Example: A Web-based and Mobile Intervention with Telephone Support for Children with Type I Diabetes: Randomized Controlled Trial Does your paper address subitem 1a-iii? * 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 brie y explain why the item is not applicable/relevant for your study The title says this is an "intervention for depression" subitem not at all important Does your paper address subitem 1b-i? * 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 brie y explain why the item is not applicable/relevant for your study The abstract describes how the intervention is a "single session intervention" and was "based on principles of cognitive-behavioral therapy and positive psychology" subitem not at all important 1 2 3 4 5 essential 1b-ii) Level of human involvement in the METHODS section of the ABSTRACT Clarify the level of human involvement in the abstract, e.g., use phrases like "fully automated" vs. "therapist/nurse/care provider/physician-assisted" (mention number and expertise of providers involved, if any). (Note: Only report in the abstract what the main paper is reporting. If this information is missing from the main body of text, consider adding it) C l e a r s e l e c t i o n Does your paper address subitem 1b-ii?
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 brie y explain why the item is not applicable/relevant for your study The manuscript describes how the intervention is "unguided" subitem not at all important 1 2 3 4 5 essential 1b-iii) Open vs. closed, web-based (self-assessment) vs. face-to-face assessments in the METHODS section of the ABSTRACT Mention how participants were recruited (online vs. o ine), e.g., from an open access website or from a clinic or a closed online user group (closed usergroup trial), and clarify if this was a purely web-based trial, or there were face-to-face components (as part of the intervention or for assessment). Clearly say if outcomes were self-assessed through questionnaires (as common in web-based trials). Note: In traditional o ine trials, an open trial (open-label trial) is a type of clinical trial in which both the researchers and participants know which treatment is being administered. To avoid confusion, use "blinded" or "unblinded" to indicated the level of blinding instead of "open", as "open" in web-based trials usually refers to "open access" (i.e. participants can self-enrol). (Note: Only report in the abstract what the main paper is reporting. If this information is missing from the main body of text, consider adding it) C l e a r s e l e c t i o n Does your paper address subitem 1b-iii?
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 brie y explain why the item is not applicable/relevant for your study Yes, the abstract states that "Participants recruited from the online workspace Prolific" subitem not at all important 1 2 3 4 5 essential 1b-iv) RESULTS section in abstract must contain use data Report number of participants enrolled/assessed in each group, the use/uptake of the intervention (e.g., attrition/adherence metrics, use over time, number of logins etc.), in addition to primary/secondary outcomes. (Note: Only report in the abstract what the main paper is reporting. If this information is missing from the main body of text, consider adding it) C l e a r s e l e c t i o n Does your paper address subitem 1b-iv?
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 brie y explain why the item is not applicable/relevant for your study "Individuals in the WLC were more likely to complete the baseline rating task (n = 417 (99.52%)) than individuals in COMET were likely to complete the COMET SSI (n = 379 (92.67%)), however, these differences were small."   [11,12]. In a digital SSI, an individual completes an an online intervention in one sitting. Meta-analyses in youth suggest that SSIs are more effective than control conditions [11,12]. SSIs also have shown promise in adults. For example, Wasil et al. [13] developed an SSI called the Common Elements Toolbox (COMET) that captures elements common to CBT and positive psychology, including behavioral activation, cognitive restructuring, selfcompassion, and gratitude. In an initial investigation, undergoing COMET was associated with improvements in perceived coping abilities and the intervention was feasible and acceptable to graduate students [13]. In the first randomized controlled trial (RCT) evaluating the efficacy of COMET, [14] reported that COMET reduced depression in undergraduate students when compared to a study skills control condition at 4-week (standardized mean difference (SMD) = 0.20) and 12-week follow-ups (SMD = 0.17)." Does your paper address CONSORT subitem 2b? * 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 brie y explain why the item is not applicable/relevant for your study "We hypothesized that COMET would lead to small improvements in depression, anxiety, well-being, functioning, and emotion regulation." 3a) Description of trial design (such as parallel, factorial) including allocation ratio 3b) Important changes to methods after trial commencement (such as eligibility criteria), with reasons Does your paper address CONSORT subitem 3a? * 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 brie y explain why the item is not applicable/relevant for your study The methods section states that this is a "two-arm parallel RCT with a 1:1 allocation ratio" Does your paper address CONSORT subitem 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 brie y explain why the item is not applicable/relevant for your study Yes, the manuscript states that "[o]ne deviation from the trial protocol is that a day before the close of the eight week assessment, we reminded participants in either treatment condition who had not yet completed the intervention that the study assessments were available in Prolific. ... The only deviation from the pre-registered [analysis] plan was that when models failed to converge, we dropped the random intercepts of time for a more parsimonious model. This occurred when examining changes in the WHO-5 and ERQ-ES in the ITT-unimputed samples and the WSAS in the ITT-imputed samples. For these analyses, we simplified the models by removing the random slopes which allowed the models to converge." subitem not at all important 1 2 3 4 5 essential 4a) Eligibility criteria for participants 3b-i) Bug fixes, Downtimes, Content Changes Bug xes, Downtimes, Content Changes: ehealth systems are often dynamic systems. A description of changes to methods therefore also includes important changes made on the intervention or comparator during the trial (e.g., major bug xes or changes in the functionality or content) (5-iii) and other "unexpected events" that may have in uenced study design such as staff changes, system failures/downtimes, etc. [2].
C l e a r s e l e c t i o n Does your paper address subitem 3b-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 brie y explain why the item is not applicable/relevant for your study No, there were no Bug fixes, Downtimes, Content Changes.
subitem not at all important 1 2 3 4 5 essential Does your paper address CONSORT subitem 4a? * 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 brie y explain why the item is not applicable/relevant for your study Yes, the manuscript states "The only inclusion criteria we used for the trial was an affirmative answer (i.e., responding "yes") to the question "Do you have -or have you hada diagnosed, on-going mental health/illness/condition?"."

4a-i) Computer / Internet literacy
Computer / Internet literacy is often an implicit "de facto" eligibility criterion -this should be explicitly clari ed. Does your paper address subitem 4a-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 brie y explain why the item is not applicable/relevant for your study Yes, the manuscript states that "No explicit exclusion criteria were used. However, it could be argued that relatively steady internet access, and internet literacy, was an entry criterion because the study required individuals to log in to Prolific 1-4 times." 4a-ii) Open vs. closed, web-based vs. face-to-face assessments: Open vs. closed, web-based vs. face-to-face assessments: Mention how participants were recruited (online vs. o ine), e.g., from an open access website or from a clinic, and clarify if this was a purely web-based 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 con rmation, phone calls) were used to detect/prevent these. Does your paper address subitem 4a-ii? * 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 brie y explain why the item is not applicable/relevant for your study Yes, the manuscript states that "Online workers living in the United States were sampled from Prolific.co, an online platform that hosts research studies." It also states that "All measures were web-based."

4a-iii) Information giving during recruitment
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. Does your paper address subitem 4a-iii?
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 brie y explain why the item is not applicable/relevant for your study Yes, the paper states that "Participants were informed that this was an Indiana University study exploring the efficacy of COMET." Does your paper address CONSORT subitem 4b? * 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 brie y explain why the item is not applicable/relevant for your study Yes, the paper states that "Online workers living in the United States were sampled from Prolific.co, an online platform that hosts research studies." subitem not at all important 1 2 3 4 5 essential 4b-i) Report if outcomes were (self-)assessed through online questionnaires Clearly report if outcomes were (self-)assessed through online questionnaires (as common in web-based trials) or otherwise.
C l e a r s e l e c t i o n Does your paper address subitem 4b-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 brie y explain why the item is not applicable/relevant for your study Yes, the report describes how "All measures were self-reported web-based assessments..." subitem not at all important 1 2 3 4 5 essential 5) The interventions for each group with sufficient details to allow replication, including how and when they were actually administered 4b-ii) Report how institutional affiliations are displayed 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 brie y explain why the item is not applicable/relevant for your study Yes, the paper describes how "Participants were informed that this was Indiana University study exploring the efficacy of COMET. No explicit exclusion criteria were used." subitem not at all important 1 2 3 4 5 essential 5-i) Mention names, credential, affiliations of the developers, sponsors, and owners Mention names, credential, a liations of the developers, sponsors, and owners [6] (if authors/evaluators are owners or developer of the software, this needs to be declared in a "Con ict of interest" section or mentioned elsewhere in the manuscript).
C l e a r s e l e c t i o n Does your paper address subitem 5-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 brie y explain why the item is not applicable/relevant for your study No, the study consent does not contain this information but the study consent does. This is a pretty standard methodology in the social sciences. The PI is not the intervention developer.
subitem not at all important 1 2 3 4 5 essential 5-ii) Describe the history/development process Describe the history/development process of the application and previous formative evaluations (e.g., focus groups, usability testing), as these will have an impact on adoption/use rates and help with interpreting results.
C l e a r s e l e c t i o n Does your paper address subitem 5-ii?
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 brie y explain why the item is not applicable/relevant for your study The manuscript does not describe in detail the development of COMET but it does refer interested readers to the paper describing the development of COMET (

5-iii) Revisions and updating
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).
C l e a r s e l e c t i o n Does your paper address subitem 5-iii?
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 brie y explain why the item is not applicable/relevant for your study The intervention is uploaded online and participants are referred to it. There is no dynamic content.

5-iv) Quality assurance methods
Provide information on quality assurance methods to ensure accuracy and quality of information provided [1], if applicable.
C l e a r s e l e c t i o n Does your paper address subitem 5-iv?
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 brie y explain why the item is not applicable/relevant for your study Yes. "Prior work suggests that inattentive or potentially fraudulent respondents may provide biased data. Following best practices in the detection of inattentive or fraudulent respondents, we used a multi-method approach to identify inattentive or potentially fraudulent respondents. First, we obtained an estimate of the time it took participants to complete the baseline portion of the study. Given that the treatment condition would be a big predictor of time spent on the study at baseline, we Z-scored the duration for each participant within each treatment conditions. Respondents taking less than 2.5 SDs to complete the first part of the study were deemed as completing the study implausibly fast. Additionally, at baseline we administered the Ten-item Personality Inventory [36], a measure of the Big Five personality traits. Because the TIPI contains 5 items that are scores in one direction (per subscale) and 5 items that are calculated in another direction, we are able to capture response inconsistency on this scale. We considered respondents as "inconsistent" if more than 40% of their responses were in an inconsistent direction. We also used the RelevantID as a third attention check and the reCaptcha score as a fourth attention check [37]. RelevantID is a proprietary algorithm that analyses the user's browser, operating system, and location to provide a fraud score ranging from 0-100 with scores greater than 30 usually understood to be bots. reCaptcha scores range from 0-1 with a higher score indicating a higher likelihood the respondent is human. Scores of 0.5 and over are generally considered human responders." subitem not at all important 1 2 3 4 5 essential 5-v) Ensure replicability by publishing the source code, and/or providing screenshots/screen-capture video, and/or providing flowcharts of the algorithms used Ensure replicability by publishing the source code, and/or providing screenshots/screencapture video, and/or providing owcharts of the algorithms used. Replicability (i.e., other researchers should in principle be able to replicate the study) is a hallmark of scienti c reporting.
C l e a r s e l e c t i o n Does your paper address subitem 5-v?
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 brie y explain why the item is not applicable/relevant for your study "The analytic plan was pre-registered in the OSF website, which also contains the data and code that produced this manuscript [1]." subitem not at all important 1 2 3 4 5 essential

5-vi) Digital preservation
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.
C l e a r s e l e c t i o n Does your paper address subitem 5-vi?
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 brie y explain why the item is not applicable/relevant for your study No. I tried doing this but they are no longer accepting preservation requests.

5-vii) Access
Access: Describe how participants accessed the application, in what setting/context, if they had to pay (or were paid) or not, whether they had to be a member of speci c group. If known, describe how participants obtained "access to the platform and Internet" [1]. To ensure access for editors/reviewers/readers, consider to provide a "backdoor" login account or demo mode for reviewers/readers to explore the application (also important for archiving purposes, see vi).
C l e a r s e l e c t i o n Does your paper address subitem 5-vii? * 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 brie y explain why the item is not applicable/relevant for your study Yes. At various points the intervention is described as "web-based." The methods section states that "The study was hosted in Qualtrics..." subitem not at all important 1 2 3 4 5 essential 5-viii) Mode of delivery, features/functionalities/components of the intervention and comparator, and the theoretical framework Does your paper address subitem 5-viii? * 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 brie y explain why the item is not applicable/relevant for your study Yes, the manuscript describes each group: "WLC: Participants assigned to the WLC control filled out the same assessment battery as participants assigned to COMET but did not have access to COMET until 8 weeks after the study. Their outcomes were not tracked following the 8-week assessment period. Because the Prolific platform requires one time estimate for the study as opposed to allowing different time estimates per condition, we attempted to make the groups somewhat more equal on the amount of time spent in the study by administering participants in the WLC additional questions assessing how important changes in depression and anxiety were to them. Specifically, once participants were assigned to the WLC, they were once again presented the items on the PHQ-9 and GAD-7, and for each of the 15 items were asked to rate how 1) important of concerning the symptom is/would be, 2) detrimental to subjective quality of life it is/would be, 3) detrimental to objective functioning it is/would be, and 4) how much they would want the symptom to improve. COMET: COMET is a 4-module intervention designed based on two core principles of CBT: cognitive restructuring and behavioral activation, and two core principles of positive psychology: gratitude and self-compassion. COMET was designed to take approximately 30-40 minutes to complete. It presents individuals with psychoeducation in the form of texts and brief exercises. Specifically, participants were shown the "ABCD" technique (for cognitive restructuring), scheduling pleasant activities (for behavioral activation), the "three good things" exercise (for gratitude), and writing self-compassionate statements (for selfcompassion

5-ix) Describe use parameters
Describe use parameters (e.g., intended "doses" and optimal timing for use). Clarify what instructions or recommendations were given to the user, e.g., regarding timing, frequency, heaviness of use, if any, or was the intervention used ad libitum.
C l e a r s e l e c t i o n Does your paper address subitem 5-ix?
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 brie y explain why the item is not applicable/relevant for your study Yes. The paper says that "Participants were advised that "[t]o get the most out of these skills, many people find it useful to practice them regularly." We recommended that participants practice at least one of the skills daily for the succeeding two week period." subitem not at all important 1 2 3 4 5 essential

5-x) Clarify the level of human involvement
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 Does your paper address subitem 5-x?
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 brie y explain why the item is not applicable/relevant for your study Yes, COMET is described as "self-guided/unguided." subitem not at all important 1 2 3 4 5 essential 5-xi) Report any prompts/reminders used Report any prompts/reminders used: Clarify if there were prompts (letters, emails, phone calls, SMS) to use the application, what triggered them, frequency etc. It may be necessary to distinguish between the level of prompts/reminders required for the trial, and the level of prompts/reminders 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 Does your paper address subitem 5-xi? * 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 brie y explain why the item is not applicable/relevant for your study Yes, the paper says "However, there were no formal reminders of skill use." subitem not at all important 1 2 3 4 5 essential 6a) Completely defined pre-specified primary and secondary outcome measures, including how and when they were assessed 5-xii) Describe any co-interventions (incl. training/support) Describe any co-interventions (incl. training/support): Clearly state any interventions that are provided in addition to the targeted eHealth intervention, as ehealth intervention may not be designed as stand-alone intervention. This includes training sessions and support [1]. It may be necessary to distinguish between the level of training required for the trial, and the level of training 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 Does your paper address subitem 5-xii? * 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 brie y explain why the item is not applicable/relevant for your study No, there were no co-interventions.
subitem not at all important 1 2 3 4 5 essential Does your paper address CONSORT subitem 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 brie y explain why the item is not applicable/relevant for your study Yes, the paper states that "The primary outcomes are depression (PHQ-9) and anxiety (GAD-7) changes at two weeks, which are given by the interaction of treatment-by-week 2, and 8 weeks, given by the treatment-by-week 8 interaction. The secondary outcomes are the 8week changes in the WHO-5, WSAS, ERQ-CR, and ERQ-ES, which are given by the interaction of treatment with week 8." 6a-i) Online questionnaires: describe if they were validated for online use and apply CHERRIES items to describe how the questionnaires were designed/deployed Does your paper address CONSORT subitem 6b? * 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 brie y explain why the item is not applicable/relevant for your study No. There were no changes to the outcomes used in the trial. 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 brie y explain why the item is not applicable/relevant for your study Yes, "We did not factor in attrition because we planned to impute data but aimed to recruit 800 individuals because we had available funding for slightly more than 788 individuals." 8a) Method used to generate the random allocation sequence NPT: When applicable, how care providers were allocated to each trial group 8b) Type of randomisation; details of any restriction (such as blocking and block size) Does your paper address CONSORT subitem 7b? * 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 brie y explain why the item is not applicable/relevant for your study There were no interim analyses. The manuscript describes the analyses in which the treatment condition is concealed.
Does your paper address CONSORT subitem 8a? * 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 brie y explain why the item is not applicable/relevant for your study 9) Mechanism used to implement the random allocation sequence (such as sequentially numbered containers), describing any steps taken to conceal the sequence until interventions were assigned 10) Who generated the random allocation sequence, who enrolled participants, and who assigned participants to interventions Does your paper address CONSORT subitem 8b? * 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 brie y explain why the item is not applicable/relevant for your study "The study was hosted in Qualtrics and randomization was performed within the Qualtrics platform which uses simple randomization. Thus, the treatment allocation schedule was concealed from the investigator and the participants." Does your paper address CONSORT subitem 9? * 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 brie y explain why the item is not applicable/relevant for your study "A study coordinator coded the treatment condition, concealing the coding scheme from the PI. For preparing all analyses associated with this study, the PI used the R [25] programming language to create a synthetic treatment variable that had no correspondence to the actual treatment assignment. Because of the nature of the intervention, actual treatment assignment could not be concealed from participants, who were the ones who assessed outcomes." 11a) If done, who was blinded after assignment to interventions (for example, participants, care providers, those assessing outcomes) and how NPT: Whether or not administering co-interventions were blinded to group assignment Does your paper address CONSORT subitem 10? * 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 brie y explain why the item is not applicable/relevant for your study "The study was hosted in Qualtrics and randomization was performed within the Qualtrics platform which uses simple randomization. Thus, the treatment allocation schedule was concealed from the investigator and the participants. A study coordinator coded the treatment condition, concealing the coding scheme from the PI. For preparing all analyses associated with this study, the PI used the R [25] programming language to create a synthetic treatment variable that had no correspondence to the actual treatment assignment. Because of the nature of the intervention, actual treatment assignment could not be concealed from participants, who were the ones who assessed outcomes." subitem not at all important 1 2 3 4 5 essential 11a-i) Specify who was blinded, and who wasn't Specify who was blinded, and who wasn't. Usually, in web-based trials it is not possible to blind the participants [1, 3] (this should be clearly acknowledged), but it may be possible to blind outcome assessors, those doing data analysis or those administering cointerventions (if any).
C l e a r s e l e c t i o n Does your paper address subitem 11a-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 brie y explain why the item is not applicable/relevant for your study "The study was hosted in Qualtrics and randomization was performed within the Qualtrics platform which uses simple randomization. Thus, the treatment allocation schedule was concealed from the investigator and the participants. A study coordinator coded the treatment condition, concealing the coding scheme from the PI. For preparing all analyses associated with this study, the PI used the R [25] programming language to create a synthetic treatment variable that had no correspondence to the actual treatment assignment. Because of the nature of the intervention, actual treatment assignment could not be concealed from participants, who were the ones who assessed outcomes." subitem not at all important 1 2 3 4 5 essential 11b) If relevant, description of the similarity of interventions (this item is usually not relevant for ehealth trials as it refers to similarity of a placebo or sham intervention to a active medication/intervention) 11a-ii) Discuss e.g., whether participants knew which intervention was the "intervention of interest" and which one was the "comparator" 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".
C l e a r s e l e c t i o n Does your paper address subitem 11a-ii?
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 brie y explain why the item is not applicable/relevant for your study "Participants were informed that this was an Indiana University study exploring the efficacy of COMET." 12a) Statistical methods used to compare groups for primary and secondary outcomes NPT: When applicable, details of whether and how the clustering by care providers or centers was addressed Does your paper address CONSORT subitem 11b? * 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 brie y explain why the item is not applicable/relevant for your study "Participants assigned to the WLC control filled out the same assessment battery as participants assigned to COMET... Because the Prolific platform requires one time estimate for the study as opposed to allowing different time estimates per condition, we attempted to make the groups somewhat more equal on the amount of time spent in the study by administering participants in the WLC additional questions assessing how important changes in depression and anxiety were to them. Specifically, once participants were assigned to the WLC, they were once again presented the items on the PHQ-9 and GAD-7, and for each of the 15 items were asked to rate how 1) important of concerning the symptom is/would be, 2) detrimental to subjective quality of life it is/would be, 3) detrimental to objective functioning it is/would be, and 4) how much they would want the symptom to improve." Does your paper address CONSORT subitem 12a? * 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 brie y explain why the item is not applicable/relevant for your study "For all outcomes (i.e., PHQ-9, GAD-7, WHO-5, WSAS, ERQ-CR, and ERQ-ES) we use linear mixed models with the lme4 [40] and lmerTest [41] to regress outcomes on: time (as a factor representing time 0, 2 weeks post-baseline, 4 weeks post-baseline, and 8 weeks postbaseline), treatment (WLC vs. COMET), and the time-by-treatment interaction. The primary outcomes are depression (PHQ-9) and anxiety (GAD-7) changes at two weeks, which are given by the interaction of treatment-by-week 2, and 8 weeks, given by the treatment-by-week 8 interaction. The secondary outcomes are the 8-week changes in the WHO-5, WSAS, ERQ-CR, and ERQ-ES, which are given by the interaction of treatment with week 8. To obtain 95% confidence intervals (CIs) on the predicted estimates by treatment and by time, we used the bootpredictlme4 package [42] to conduct 1,000 bootstrap samples to obtain 95% CIs on the predicted group scores over time.
Standardized effect sizes were calculated using the method suggested by Feignhold [43] which involves dividing the estimated difference between treatment and control at the different time points by the standard deviation of the baseline assessment on each measure. To calculate the 95% CI on these d-type effect sizes, we used the "cohen.d.ci" function in the psych package [44]." subitem not at all important 1 2 3 4 5 essential 12a-i) Imputation techniques to deal with attrition / missing values 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]).
C l e a r s e l e c t i o n 12b) Methods for additional analyses, such as subgroup analyses and adjusted analyses Does your paper address subitem 12a-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 brie y explain why the item is not applicable/relevant for your study "Missing data imputation. Missing data in demographic covariates was minimal (see Table  1), with most individuals providing complete information for most variables. There was more data missing for the longitudinal outcomes (i.e., PHQ-9, GAD-7, WHO-5, WSAS, ERQ).
To address missing data, including missing outcome data, we imputed all missing data using a machine learning algorithm: non-parametric missing value imputation using random forests, with the R package missForest [45]. To preserve the association between the variables [46], we did not pre-process variables and only minimally recoded them. Imputation models that use multiple variables are often preferable to last observation carried forward-type imputation models [47,48]. The variables in the imputation model included the baseline demographics (see Table 1) and week 2, 4, and 8 scores on the PHQ-9, GAD-7, WHO-5, WSAS, ERQ.
The analytic plan was repeated three different times. The first time followed an "intent to treat" (ITT) approach with all individuals who were randomized and without imputed any outcomes (ITT-unimputed). The second time used an ITT approach as well but missing outcome data were imputed as described above (ITT-imputed). Once the results with the ITT-unimputed and ITT-imputed data were clear, the PI was "unblinded" from the treatment assignment to construct the third sample: the "per protocol" sample. The PP sample included individuals only if they followed the intervention all though to the end (i.e., they were not just randomized but completed the condition they were assigned to)."

X26) REB/IRB Approval and Ethical Considerations [recommended as subheading under "Methods"] (not a CONSORT item)
subitem not at all important 1 2 3 4 5 essential Does your paper address CONSORT subitem 12b? * 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 brie y explain why the item is not applicable/relevant for your study "To control for the possibility that our results are accounted for by inattentive respondents, we removed all participants who had failed even a single attention check leaving us with a sample of 787 individuals (WLC = 404, COMET-SSI = 383). Across the three time points (weeks 2, 4, and 8), six outcomes (i.e., depression, anxiety, well-being, functioning, cognitive reappraisal, and expressive suppression), and three datasets (i.e., imputed, unimputed, and per protocol), removing inattentive participants did not change the pattern of results." Does your paper address subitem X26-i?

X26-i) Comment on ethics committee approval
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 brie y explain why the item is not applicable/relevant for your study "This is a randomized controlled trial (RCT) approved by the institution's internal review board."

x26-ii) Outline informed consent procedures
Outline informed consent procedures e.g., if consent was obtained o ine or online (how? Checkbox, etc.?), and what information was provided (see 4a-ii). See [6] for some items to be included in informed consent documents. Does your paper address subitem X26-ii?
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 brie y explain why the item is not applicable/relevant for your study "Online workers living in the United States were sampled from Prolific.co, an online platform that hosts research studies. The only inclusion criteria we used for the trial was an affirmative answer (i.e., responding "yes") to the question "Do you have -or have you hada diagnosed, on-going mental health/illness/condition?". Based on this inclusion criteria, and sampling online from the United States, 14,628 individuals were eligible for the study. Participants were informed that this was an Indiana University study exploring the efficacy of COMET. No explicit exclusion criteria were used. However, it could be argued that relatively steady internet access, and internet literacy, was an entry criterion because the study required individuals to log in to Prolific 1-4 times."

X26-iii) Safety and security procedures
Safety and security procedures, incl. privacy considerations, and any steps taken to reduce the likelihood or detection of harm (e.g., education and training, availability of a hotline) 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 brie y explain why the item is not applicable/relevant for your study This is a very minimal risk intervention but like most of these studies that are done in fully remote samples we cannot control what participants do during the intervention.
Does your paper address CONSORT subitem 13a? * 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 brie y explain why the item is not applicable/relevant for your study Does your paper address CONSORT subitem 13b? (NOTE: Preferably, this is shown in a CONSORT flow diagram) * 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 brie y explain why the item is not applicable/relevant for your study No participants were excluded from analyses.

13b-i) Attrition diagram
Strongly recommended: An attrition diagram (e.g., proportion of participants still logging in or using the intervention/comparator in each group plotted over time, similar to a survival curve) or other gures or tables demonstrating usage/dose/engagement.
C l e a r s e l e c t i o n Does your paper address subitem 13b-i?
Copy and paste relevant sections from the manuscript or cite the gure 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 brie y explain why the item is not applicable/relevant for your study "A total of 861 individuals began the study but 33 did not complete the baseline screening (see Figure 1)." Does your paper address CONSORT subitem 14a? * 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 brie y explain why the item is not applicable/relevant for your study "There were no statistically-significant differences between the treatment conditions in the rate of return for the 2-week assessment on July 19-21 2022 (χ^2(1) = 0, P = 0.99), 4-week assessment on August 2-4 2022 (χ^2(1) = 1.12, P = 0.29), or 8-week assessment on August 30-September 3 2022 (χ^2(1) = 0.19, P = 0.66)." This is also in the "Methods" section.

14a-i) Indicate if critical "secular events" fell into the study period
Indicate if critical "secular events" fell into the study period, e.g., signi cant changes in Internet resources available or "changes in computer hardware or Internet delivery resources" Does your paper address subitem 14a-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 brie y explain why the item is not applicable/relevant for your study No specific thing like that happened to our knowledge. Interested readers can look at the study dates and decide for themselves.
Does your paper address CONSORT subitem 14b? * 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 brie y explain why the item is not applicable/relevant for your study This is not applicable to the current study.
subitem not at all important 1 2 3 4 5 essential Does your paper address CONSORT subitem 15? * 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 brie y explain why the item is not applicable/relevant for your study "  Does your paper address subitem 15-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 brie y explain why the item is not applicable/relevant for your study "

16-i) Report multiple "denominators" and provide definitions 16
Report multiple "denominators" and provide de nitions: 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 speci c pre-de ned time points of interest (in absolute and relative numbers per group). Always clearly de ne "use" of the intervention.
C l e a r s e l e c t i o n Does your paper address subitem 16-i? 16 * 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 brie y explain why the item is not applicable/relevant for your study "Intent to treat (ITT) sample-unimputed (WLC: n = 419, COMET: n =409) ... Table 2: Changes over time in depression, anxiety, well-being, functioning, and emotion regulation in 828 participants randomized 1:1 to a single-session intervention vs. a waiting list control by inattentive status in the ITT-unimputed sample" ... ITT-imputed (WLC: n = 419, COMET: n =409) ... 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 brie y explain why the item is not applicable/relevant for your study "The analytic plan was repeated three different times. The first time followed an "intent to treat" (ITT) approach with all individuals who were randomized and without imputed any outcomes (ITT-unimputed). The second time used an ITT approach as well but missing outcome data were imputed as described above (ITT-imputed). Once the results with the ITT-unimputed and ITT-imputed data were clear, the PI was "unblinded" from the treatment assignment to construct the third sample: the "per protocol" sample. The PP sample included individuals only if they followed the intervention all though to the end (i.e., they were not just randomized but completed the condition they were assigned to)." subitem not at all important 1 2 3 4 5 essential Does your paper address CONSORT subitem 17a? * 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 brie y explain why the item is not applicable/relevant for your study " Figure 2. Standardized mean differences (SMDs) between the single-session intervention COMET and a waiting list control in the unimputed (A) and imputed (B) data (N=828)"

17a-i) Presentation of process outcomes such as metrics of use and intensity of use
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 de nitions 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 de ned (e.g., timeout after idle time) [1] (report under item 6a).
C l e a r s e l e c t i o n 17b) For binary outcomes, presentation of both absolute and relative effect sizes is recommended 18) Results of any other analyses performed, including subgroup analyses and adjusted analyses, distinguishing pre-specified from exploratory Does your paper address subitem 17a-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 brie y explain why the item is not applicable/relevant for your study No. This was a single session intervention. We assume that participants who completed the intervention received an adequate dose of it.
Does your paper address CONSORT subitem 17b? * 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 brie y explain why the item is not applicable/relevant for your study No. The trial does not report on any binary outcomes.
subitem not at all important 1 2 3 4 5 essential Does your paper address CONSORT subitem 18? * 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 brie y explain why the item is not applicable/relevant for your study "To control for the possibility that our results are accounted for by inattentive respondents, we removed all participants who had failed even a single attention check leaving us with a sample of 787 individuals (WLC = 404, COMET-SSI = 383). Across the three time points (weeks 2, 4, and 8), six outcomes (i.e., depression, anxiety, well-being, functioning, cognitive reappraisal, and expressive suppression), and three datasets (i.e., imputed, unimputed, and per protocol), removing inattentive participants did not change the pattern of results.
The largest intervention effect for depression was at week 4 in the per protocol sample, representing a very small effect (B = -0.63, 95% CI: -1.26, -0.01; p=0.046). Nonetheless, this was a very small effect that was not consistent across the datasets or timepoints. Similarly, there was some evidence for a reduction of expressive suppression in COMET relative to the WLC at week 2 (B = 0.11, 95% CI: -0.02, 0.24; p=0.089) but this was a small effect (SMD = 0.07, 95% CI: -0.07, 0.21)."

18-i) Subgroup analysis of comparing only users
A subgroup analysis of comparing only users is not uncommon in ehealth trials, but if done, it must be stressed that this is a self-selected sample and no longer an unbiased sample from a randomized trial (see 16-iii Does your paper address subitem 18-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 brie y explain why the item is not applicable/relevant for your study No. We are not interested in doing this. As the statement notes this is an unrandomized sample.
Does your paper address CONSORT subitem 19? * 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 brie y explain why the item is not applicable/relevant for your 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 brie y explain why the item is not applicable/relevant for your study No. We collected qualitative data from participants but have yet to analyze it because it was not specified as an outcome in the study.

22)
Interpretation consistent with results, balancing benefits and harms, and considering other relevant evidence NPT: In addition, take into account the choice of the comparator, lack of or partial blinding, and unequal expertise of care providers or centers in each group subitem not at all important 1 2 3 4 5 essential 22-i) Restate study questions and summarize the answers suggested by the data, starting with primary outcomes and process outcomes (use) Restate study questions and summarize the answers suggested by the data, starting with primary outcomes and process outcomes (use). Does your paper address subitem 22-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 brie y explain why the item is not applicable/relevant for your study "We conducted an RCT comparing the SSI COMET to a WLC in online workers. Our study was powered to detect rather small differences between the treatment conditions. The sample showed elevated levels of depression and anxiety with most individuals being flagged on a screening scale for depression, anxiety, or poor functioning. Our results, however, did not suggest statistical or clinically-significant differences between COMET and the WLC in any of the psychologically-relevant outcomes we assessed, despite most individuals completing the intervention. Given that our study was powered to detect small differences, we must conclude that if the COMET SSI has effects in online workers, the effects are so small so as to be clinically meaningless."

22-ii) Highlight unanswered new questions, suggest future research
Highlight unanswered new questions, suggest future research. 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 brie y explain why the item is not applicable/relevant for your study "it is possible that interventions that are more targeted to them (e.g., with personalized content) may be effective in this patient group. ... These findings, and ours, may be taken to suggest there needs to be more care in the design of trials of SSIs in relation to the populations and clinical problems targeted. For some clinical problems and some populations, SSIs may be effective irrespective of what active mechanisms the interventions target. Alternatively, data-driven approaches may help identify subgroups of individuals who preferentially respond to specific SSI [5,6,60,61]."

20-i) Typical limitations in ehealth trials
Typical limitations in ehealth trials: Participants in ehealth trials are rarely blinded. Ehealth trials often look at a multiplicity of outcomes, increasing risk for a Type I error. Discuss biases due to non-use of the intervention/usability issues, biases through informed consent procedures, unexpected events. Does your paper address subitem 20-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 brie y explain why the item is not applicable/relevant for your study "Finally, typical limitations of web-based trials apply to the current study including the lack of concealment of intervention condition to the participant as well as the reliance on selfreport measures apply to the current study."

21-i) Generalizability to other populations
Generalizability to other populations: In particular, discuss generalizability to a general Internet population, outside of a RCT setting, and general patient population, including applicability of the study results for other organizations Does your paper address subitem 21-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 brie y explain why the item is not applicable/relevant for your study "First, we recruited online workers for this study. Online workers have been noted as a population at high risk for depression [17]. While our results cast doubt on the efficacy of COMET for this target population, it is possible that interventions that are more targeted to them (e.g., with personalized content) may be effective in this patient group. Additionally, we recruited participants if they had an "ongoing/diagnosed" mental health condition. Although the scores on the clinical screening scales suggest that most people would have met criteria for a depressive or anxiety disorder, it is possible that we recruited many individuals who would not have benefited from treatment for depression or anxiety and may have benefited from other interventions (e.g., substance use treatment, insomnia treatment)."

21-ii) Discuss if there were elements in the RCT that would be different in a routine application setting
Discuss if there were elements in the RCT that would be different in a routine application setting (e.g., prompts/reminders, more human involvement, training sessions or other cointerventions) and what impact the omission of these elements could have on use, adoption, or outcomes if the intervention is applied outside of a RCT setting. Does your paper address subitem 21-ii?
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 brie y explain why the item is not applicable/relevant for your study "We did not recruit participants help-seeking in routine care and instead provided treatment to individuals with mental health problems. However, Zhao et al. [49] recently reported that psychological interventions can be effective even when individuals are not seeking treatment. Additionally, while Prolific is renowned for its data quality [50], and we reviewed participants' responses for data quality, we have no way of confirming that respondents honestly engaged with the material." Does your paper address CONSORT subitem 23? * 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 brie y explain why the item is not applicable/relevant for your study Yes, at various points including the abstract the manuscript cites the National Clinical Trials registry. The number is "NCT05379881."