Data Analysis
Data analysis was performed with SPSS (version 26.0; IBM Corp). The participants were analyzed based on their initial assigned group. Data cleaning and error checking were performed before analysis. Median and IQR were used to summarize the nonnormally distributed data for continuous variables, while frequencies and percentages were used to report the categorical variables. The comparison of baseline characteristics between the 2 arms was conducted using the Mann-Whitney test for continuous variables and chi-square for categorical variables. A generalized linear mixed model (GLMM) was used to assess the group, time, and group and time interaction effect on the intention and willingness to sext, knowledge, attitude, perceived norms, and prototype perceptions between the 2 groups before and after controlling for covariates (age, sex, relationship status, and the amount of time spent on the web).