Analyses
As the primary population, the full analysis set (FAS), excluding the scores of those who did not respond to T1 from all randomized participants, was used in all analyses, except process and feasibility evaluation. The per-protocol set (PPS), which excluded participants who did not respond on time, those who did not complete watching video on time in the intervention group, and those who withdrew from the study, was also defined for sensitivity analysis of the primary outcome.Baseline characteristics are summarized as mean and standard deviation for continuous variables and frequency and proportion for categorical variables. Student’s t-test, chi-square test, and Fisher’s exact test were performed for comparisons between the intervention and control groups.The difference in the Sense of Coping Difficulty subscale at T3 between groups was evaluated by a t-test on cluster-specific means. As a sub-analysis, a multilevel analysis with a mixed model was performed, with group as fixed effects, and school as random effects, adjusting for some baseline characteristics. We fitted a mixed model for repeated measures (MMRM), with group, time points (T1, T2, and T3) and their interactions as fixed effects, and schools and study participants as random effects.The three actual behavioral and attitude items were compared between the groups using chi-square analysis. A multilevel analysis was then conducted using a mixed-effects logistic model.For the 10 knowledge items, the percentage of correct answers for each item was compared between the groups using chi-square analysis or Fisher's exact test. The total number of correct answers was compared using a Wilcoxon rank-sum test. Mixed-effect logistic models were also fitted.For program goal achievement, the medians and interquartile ranges of the scores and the total scores for each item were calculated and compared, using the Wilcoxon rank-sum test. MMRM were also fitted.In an exploratory manner, we examined the interaction between the baseline score and intervention effects on the Sense of Coping Difficulty subscale.The open-ended text response was analyzed qualitatively as part of a process evaluation. We created classification axes based on similarity and separated them into the smallest units whose meanings could be understood [The missing data were not imputed. A p-value of 0.05 or less was considered significant. All analyses were performed using SAS9.4 (SAS Institute Inc., Cary, NC, USA).