Data analyses
MP
REGRESSION
Characteristics of participants at baseline were reported for the overall sample and separately for the three exposure groups. Counts and proportions were reported for categorical characteristics.The numerical data on public stigma, motivation to change one’s own alcohol use, motivation to talk to someone else about their alcohol use, motivation to seek information about AUD treatment, motivation to seek AUD treatment and self-stigma were analyzed by mixed effects linear regression. The models included a fixed effect for group randomized to, a fixed effect for time point (baseline and follow-up) and a fixed effects interaction between group and time point. As baseline measurements were obtained before randomization, groups at baseline were modelled as a separate common treatment category, constraining baseline measurements to no systematic treatment effect between the groups. All mixed models included a random intercept for each participant. Normality assumptions were evaluated visually, and deviations were handled by repeating the analysis with nonparametric bootstrapping. Using the maximum likelihood estimator and assuming the dropout mechanism is ‘missing at random’, linear mixed models deal efficiently with missing values. Estimates were calculated with 95% confidence intervals (CI). Cohen’s As the results on motivation to change own alcohol use showed the opposite result from a priori hypothesis, post hoc analyses were performed to understand the findings more fully. First, the sample was stratified into two, according to level of motivation at baseline, where the participants who scored in 75th percentile or higher were grouped into the high motivation-group and compared to the participants who scored in the 74th percentile and lower. Second, the sample was stratified according to level of alcohol use according to the AUDIT-C – one group with participants with low-risk alcohol use, and one group with participants with hazardous alcohol use.All analyses were carried out using Stata MP 16.1 (StataCorp LP, College Station, TX). The blinding of which video the participants saw, was not broken until the analyses were completed.