PONE-D-24-51154A cluster randomised controlled trial investigating the effectiveness of the‘Support group’ intervention in primary schools in Norway: a study protocolPLOS ONE

Dear Dr. Valla,

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Academic Editor

PLOS ONE

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Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. Does the manuscript provide a valid rationale for the proposed study, with clearly identified and justified research questions?

The research question outlined is expected to address a valid academic problem or topic and contribute to the base of knowledge in the field.

Reviewer #1: Partly

Reviewer #2: Yes

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2. Is the protocol technically sound and planned in a manner that will lead to a meaningful outcome and allow testing the stated hypotheses?

The manuscript should describe the methods in sufficient detail to prevent undisclosed flexibility in the experimental procedure or analysis pipeline, including sufficient outcome-neutral conditions (e.g. necessary controls, absence of floor or ceiling effects) to test the proposed hypotheses and a statistical power analysis where applicable. As there may be aspects of the methodology and analysis which can only be refined once the work is undertaken, authors should outline potential assumptions and explicitly describe what aspects of the proposed analyses, if any, are exploratory.

Reviewer #1: Partly

Reviewer #2: Yes

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3. Is the methodology feasible and described in sufficient detail to allow the work to be replicable?

Descriptions of methods and materials in the protocol should be reported in sufficient detail for another researcher to reproduce all experiments and analyses. The protocol should describe the appropriate controls, sample size calculations, and replication needed to ensure that the data are robust and reproducible.

Reviewer #1: Yes

Reviewer #2: Yes

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4. Have the authors described where all data underlying the findings will be made available when the study is complete?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception, at the time of publication. The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #1: Yes

Reviewer #2: No

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5. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #1: Yes

Reviewer #2: Yes

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6. Review Comments to the Author

Please use the space provided to explain your answers to the questions above and, if applicable, provide comments about issues authors must address before this protocol can be accepted for publication. You may also include additional comments for the author, including concerns about research or publication ethics.

You may also provide optional suggestions and comments to authors that they might find helpful in planning their study.

(Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: This manuscript presents a study protocol for a cluster randomized controlled trial (CRCT) investigating the effectiveness of a support group intervention for bullying in Norwegian primary schools. While the study addresses an important topic and the chosen methodology is generally appropriate, several aspects of the protocol require clarification and strengthening before the study commences. The rationale for the intervention is well-articulated, but the description of the intervention itself lacks sufficient detail.

The description of the Support Group intervention is too general. While the principles of the solution-focused approach (SFA) are mentioned, the specific activities and procedures within the support group sessions are not clearly outlined.

Table 1 provides a basic overview, but it lacks detail regarding the content and duration of each step. How are the "suggestions to help the bullied child" generated and implemented? How is progress monitored and evaluated within the SFA framework? A more detailed manual or protocol for the intervention is needed to ensure fidelity and replicability.

While the manuscript lists the chosen outcome measures, it lacks a detailed explanation of how these measures will be used to answer the research questions. For instance, how will the Olweus questionnaire be used to measure a reduction in bullying (pRQ1)? Will changes in scores be analyzed, or specific items related to bullying frequency? Similarly, which specific domains of the KIDscreen-27 and SDQ will be used to address the research questions related to quality of life and mental health? Clearer links between the research questions and the specific aspects of the outcome measures are needed.

The analysis plan is too brief. While generalized mixed models (GLM) are mentioned, the specific models to be used for each research question are not specified. Which covariates will be included in the models? How will the clustering effect be accounted for in the analysis? Will interaction effects between intervention type and time be explored? A more detailed description of the statistical analysis plan, including the specific models and variables, is required. The rationale for using an unstructured covariance matrix should also be justified. Given the longitudinal nature of the data, exploring alternative covariance structures might be warranted. Furthermore, the plan to address missing data using multiple imputation is appropriate, but the specific imputation model and assumptions should be described.

The process evaluation plan is a strength of the protocol, but it could be further developed. While the manuscript mentions collecting data on fidelity, acceptability, and contextual factors, the specific methods for collecting these data are not clearly described. What specific questions will be asked in the focus groups and interviews? How will the qualitative data be analyzed? A more detailed description of the data collection and analysis methods for the process evaluation is needed. Furthermore, how will the findings from the process evaluation be integrated with the outcome evaluation to understand the intervention's effectiveness?

The rationale for the sample size calculation at the individual child level needs further clarification. The manuscript mentions expecting a change of 3 points in the "social support and peers" domain of KIDscreen-27. However, the basis for this assumption is not provided. Providing a reference or justification for this expected change would strengthen the sample size calculation.

While the rationale for using "usual care" as the control is provided, a more detailed description of what "usual care" entails in the participating schools is needed.

The manuscript mentions informing parents about the support groups. However, it is unclear whether active consent will be obtained from parents for their children to participate in the support groups. Clarifying the consent process for both the overall study and the support groups is important.

While blinding of participants and intervention providers is not feasible, the manuscript should clarify whether the individuals conducting the baseline and follow-up assessments will be blinded to group allocation.

Overall comments: Providing more detail about the intervention, outcome measures, analysis plan, and process evaluation will significantly strengthen the protocol and enhance the rigor and interpretability of the study's findings. This study has the potential to contribute valuable knowledge to the field of bullying prevention, and addressing these concerns will ensure that the study is conducted to the highest scientific standards.

Reviewer #2: 1. I would encourage authors to provide a conceptual framework for this support group intervention addressing bullying prevention.

Suggestions that you can consider what to include: Theory (Bronfenbrenner’s Ecological Systems Theory) → Components (which construct from theory will work on which component) → Mediators/causal factors → Outcomes (both proximal and distal outcome).

2. Add a separate section for ‘Measures’ for each of the scales to be used for this trial. Are all those scales validated in Norwegian?

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Reviewer #1: No

Reviewer #2: No

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A cluster randomised controlled trial investigating the effectiveness of the

‘Support group’ intervention in primary schools in Norway: a study protocol

PONE-D-24-51154R1

Dear Dr. Valla,

We’re pleased to inform you that your manuscript has been judged scientifically suitable for publication and will be formally accepted for publication once it meets all outstanding technical requirements.

Within one week, you’ll receive an e-mail detailing the required amendments. When these have been addressed, you’ll receive a formal acceptance letter and your manuscript will be scheduled for publication.

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Kind regards,

Alejandro Botero Carvajal, MD

Academic Editor

PLOS ONE

Additional Editor Comments (optional):

Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. Does the manuscript provide a valid rationale for the proposed study, with clearly identified and justified research questions?

The research question outlined is expected to address a valid academic problem or topic and contribute to the base of knowledge in the field.

Reviewer #3: Yes

Reviewer #4: Yes

**********

2. Is the protocol technically sound and planned in a manner that will lead to a meaningful outcome and allow testing the stated hypotheses?

The manuscript should describe the methods in sufficient detail to prevent undisclosed flexibility in the experimental procedure or analysis pipeline, including sufficient outcome-neutral conditions (e.g. necessary controls, absence of floor or ceiling effects) to test the proposed hypotheses and a statistical power analysis where applicable. As there may be aspects of the methodology and analysis which can only be refined once the work is undertaken, authors should outline potential assumptions and explicitly describe what aspects of the proposed analyses, if any, are exploratory.

Reviewer #3: Yes

Reviewer #4: Yes

**********

3. Is the methodology feasible and described in sufficient detail to allow the work to be replicable?

Descriptions of methods and materials in the protocol should be reported in sufficient detail for another researcher to reproduce all experiments and analyses. The protocol should describe the appropriate controls, sample size calculations, and replication needed to ensure that the data are robust and reproducible.

Reviewer #3: Yes

Reviewer #4: Yes

**********

4. Have the authors described where all data underlying the findings will be made available when the study is complete?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception, at the time of publication. The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #3: Yes

Reviewer #4: Yes

**********

5. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #3: Yes

Reviewer #4: Yes

**********

6. Review Comments to the Author

Please use the space provided to explain your answers to the questions above and, if applicable, provide comments about issues authors must address before this protocol can be accepted for publication. You may also include additional comments for the author, including concerns about research or publication ethics.

You may also provide optional suggestions and comments to authors that they might find helpful in planning their study.

(Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #3: I encourage the author to carry out more in-depth research, which is very meaningful for reducing campus bullying.

Reviewer #4: I consider that the study meets the fundamental requirements to be considered a good work and the comments and their respective proposals for improvement raised by the people who have carried out the review have been taken into account.

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7. PLOS authors have the option to publish the peer review history of their article (what does this mean? ). If published, this will include your full peer review and any attached files.

If you choose “no”, your identity will remain anonymous but your review may still be made public.

Do you want your identity to be public for this peer review? For information about this choice, including consent withdrawal, please see our Privacy Policy .

Reviewer #3: No

Reviewer #4: No

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