Crystal Smit

An Integrated Model 3 51 METHOD Participants The first four data-collection waves employed data from the MyMovez research program (MyMovez, 2017). The aim of this research program was to unravel young adolescents’ social network structures in combination with individual, psychosocial, and other environmental factors related to energy intake and expenditure (see Bevelander et al., 2018 for a detailed description of the research program). The current sample of the study consists of 953 young adolescents who participated in at least one of the four data-collection waves. All schools following a regular education program were eligible for participation. The initial age of the participants ranged between 8 and 15 years, with a mean age of 11.19 years ( SD = 1.36). Boys and girls were represented about equally: 53.9% of the participants were girls. Of the total sample, 453 (47.5%) participants attended primary school and 500 (52.5%) attended secondary school. The majority of the participants were of Dutch origin ( > 90%). Most of the participants had normal weight (74.4%); 7.8% were underweight, 14.2% were overweight, and 3.6% were extremely overweight, that is, obese (Talma, Schonbeck, Bakker, Hirasing, & Van Buuren, 2010). Procedure Participants were recruited through their primary and secondary schools. After gaining permission to participate from the schools’ directors, activewritten consent was obtained from participants’ caretakers and the participants themselves. At the start of each data-collection wave, new participants had the opportunity to participate in the MyMovez research program (MyMovez, 2017), In addition, some participants dropped out during data collection, which resulted in different sample sizes for each data wave. Data collection for the baseline assessment (T1) took place in February 2016. Measurements for the second (T2), third (T3), and fourth (T4) waves took place in April 2016, June 2016, and February 2017, respectively. The number of participating young adolescents was 792 at T1, 852 at T2, 824 at T3, and 671 at T4.