Miller 2023.

Study characteristics
Methods	Study design: cluster‐RCT Study grouping: parallel group Cluster size: 2 (parent level) Study duration: 12 weeks
Participants	Inclusion criteria: Arabic‐speaking Syrian refugee or host community families with ≥ 1 child aged 3–12 years; both primary caregivers willing to commit to attending all sessions of the CSI if randomised to the intervention arm of the study; not having participated in a parenting or stress management intervention previously Exclusion criteria: not reported Age range: children: 3–12 years; mean age of caregivers: 37.4 years Gender: not reported for both the adult and the children population Intervention sample: 240 Control sample: 240 Main type of traumatic event: displacement Phase of humanitarian crisis: during the acute crisis (mortality is still higher than it was before the crisis). The study took place between July 2019 and spring 2020. Type of humanitarian crisis: war/armed conflict
Interventions	Intervention name: Caregiver Support Intervention (CSI) Delivered by: para‐professionals: 20 facilitators were non‐specialist providers, including 10 Syrians, 9 Lebanese, and 1 Palestinian, with an equal number of women and men Format of therapy: face to face Number of sessions (total): 9 Type of control: waiting list Type of intervention context: group intervention – offices of 3 community‐based organisations with which War Child Holland collaborates in the target communities Type of promotion intervention: group level Description of the intervention: the CSI was a 9‐session, weekly selective preventive group intervention, co‐facilitated by trained and supervised non‐mental health specialists. Groups were offered separately to women and men, with 10–12 participants per group (see also Miller 2020).
Outcomes	To account for clustering at the family level, the intraclass correlation was estimated at 0.15. Mental well‐being Outcome type: continuous outcome Reporting: fully reported Scale: Warwick‐Edinburgh Mental Wellbeing Scale (WEMWBS) Direction: higher is better Data value: endpoint, 3‐month follow‐up Acceptability (dropout from trial) Outcome type: dichotomous outcome Reporting: fully reported Data value: endpoint
Notes	Sponsorship source: grants from the ELMA Creative Foundations, the Open Societies Foundation, and the Fred Foundation. Country: Lebanon Setting: Tripoli in North Lebanon Author's name: Kenneth E Miller Institution: University of British Columbia Email: kenneth.miller@warchild.nl Address: 2125 Main Mall Vancouver, BC, V6T 1Z4, Canada
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Quote: "A block randomization design was used, using a participatory methodology implemented successfully in our pilot RCT. At baseline assessment, after completing the questionnaires, one caregiver from each family was asked to draw a lollipop out of an opaque bag, filled with an equal number of red and green lollipops to ensure an equal number of CSI and wait list control participants. After baseline data were completed, a coin toss determined the meaning of each color, CSI or WLC. This process resulted in an equal number of CSI and WLC families in each wave."
Allocation concealment (selection bias)	Low risk	The group assignment was concealed until a coin was flipped.
Blinding of participants and personnel (performance bias) All outcomes	High risk	Quote: "Coordinators were not blind to group assignment, as they were involved in scheduling participants into CSI groups. Given the nature of the study, participants and group facilitators were not blind to group assignment."
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Quote: "The lead investigators, trial statisticians and Research Assistants (RAs) remained blind to group assignment throughout the study."
Incomplete outcome data (attrition bias) All outcomes	Low risk	Attrition < 10% in both study arms.
Selective reporting (reporting bias)	Low risk	All measures described in the methods section of the article were also reported in the results. No trial protocol available but trial registered at the ISRCTN registry (prospective trial registration: ISRCTN22321773).
Therapist qualification	Low risk	Quote: "All prospective facilitators participated in a six‐day training, followed by three on‐site observations and weekly supervision by a social worker experienced in psychosocial interventions in humanitarian settings, who in turn was supervised remotely by a clinical psychologist [KM]."
Therapist/investigator allegiance	Unclear risk	No information provided.
Intervention fidelity	Low risk	Quote: "Implementation fidelity was assessed with a fidelity checklist, which was completed by the co‐facilitators following each session.
Other bias	Low risk	No other sources of bias detected. Cluster‐RCT risk of bias extension 1. Recruitment bias; the recruited population belonged to the same catchment area (low risk of bias) 2. Baseline imbalance; cluster balance was maintained after randomisation (low risk of bias) 3. Loss of clusters; < 10% of the clusters were lost (low risk of bias) 4. Incorrect analysis; the analyses were correctly conducted and reported (low risk of bias)