Statistical analysis
First, the regression-residual adjustment method [The ICC results for changes in intrinsic motivation was .08, and for autonomous extrinsic motivation changes it was .09. These results indicated that between-school variability accounted for a maximum of 9% of the variance in adolescents’ scores for the motivation variables. Based on the criteria set by Murray [Model A:Level-1 model:Level-2 model:Model B:Level 1 model:Level 2 model:The purpose of the second research question was to examine the influences of intrinsic interest change, and autonomous extrinsic motivation change on the changing MVPA trajectories. Thus, the intrinsic interest change, and autonomous extrinsic motivation change were included in the level-2 model. Model C, as shown below, was constructed and tested to answer the second research question.Model C:Level 1 model:Level 1 model: Level 2 model:In Model A, B, and C, the time variable was centered on the first measurement of adolescent daily MVPA. In other words, the first time point was coded as 0. In Model A, B, and C, π