Crystal Smit

Chapter 4 70 METHODS Design The study involved a three-arm cluster randomized controlled trial with schools as the unit of randomization. The schools were randomly assigned to either the (1) existing social network intervention (called Share H 2 O ), (2) active control condition or (3) control condition by a random allocation algorithm. In the social network intervention, children were exposed to peers from their own classroom who were identified and trained as influence agents to promote water consumption as an alternative to SSB consumption. The active control condition was based on the principles of mass media campaigns and, therefore, consisted of exposing all children simultaneously to a presentation on the benefits of water consumption. The required sample size was based on the previous pilot study (Smit et al., 2016) where a small effect of the social network intervention was found with 210 children with a social network intervention condition and control condition. This number was multiplied with 1.5 to add the third condition (i.e., active control) in the current study, resulting in a minimum number of 315 children across the three groups. In order to take non-response in the active consent procedure into account, a larger number of children were recruited. Procedure The study took place from February to June 2018 and consisted of three assessments: baseline (February–March 2018; T1), immediately after the start of the intervention (April–May 2018; T2) and during a follow-up four weeks later (June–July 2018; T3). At each assessment, children received a smartphone with a pre-installed research application and an activity-tracking bracelet for seven days (Bevelander et al., 2018; MyMovez, 2017). Via the research application, children received questionnaires and were also able to chat and to share pictures and short videos with peers. At T1, children completed drinking-related measures and sociometric nominations. Identical measures were assessed at T2 and T3. To assess whether children were aware of the actual purpose of the study, they were asked at T3 to describe what they believed to be the purpose of the study. None