Data Preparation
REGRESSION, ATTRITION
The trait outcomes data set across conditions had 0.32% (356/112,667) missing item responses at T1, 4.31% (4858/112,667) missing item responses at T2, and 3.12% (3517/112,667) missing item responses at T3 (Independent sample Moreover, the dropout rate never exceeded 5% between time points for any of the variables, supporting the conclusion that missing data were not concerning for this data set, given the high retention rates [For hypothesis testing, LMMs and post hoc ANCOVAs were conducted on an intention-to-treat basis without performing data imputation. As the percentage of missingness was <5%, LMMs and ANCOVAs were considered robust against a noncomplete data set [The LMMs and ANCOVAs assumptions of the linearity of residuals, continuous dependent variables, homogeneity of regression slopes, homogeneity of covariance matrices, and absence of collinearity were all met for the trait outcomes. The assumption of homoscedasticity was met for all trait outcomes, with only a slight violation of the internalization scores. Despite not meeting perfect normality, all residuals of the trait outcomes at T2 and T3 presented only minimal skewness (−2<skewness<+2) and minimal kurtosis (excess kurtosis <5). Given that ANCOVA is robust against the violation of the normal distribution of residuals when conducted with an appropriate sample size and groups of equal size, the data were neither transformed nor were outlier scores substituted [Attrition rates were also low for state outcomes. For the intervention group only, missing responses on the 1-item state measures ranged between 12.1% (112‬/924; before video 1) and 13.8% (128/924; after video 6) for body satisfaction and between 12% (111‬/924; before video 1) and 14% (129/924; after video 6) for mood (