Statistical Analysis
REGRESSION, RECRUITMENT
Statistical analyses were performed using Stata/IC statistical software version 15.1 (StataCorp). For cessation analysis, we used the 7-day point prevalence cessation that was self-reported by participants at 6 months as the outcome variable and used logistic regression and intent-to-treat analysis (ie, participants were analyzed according to their original study groups assigned by randomization). The 3 subhypotheses of H1 were analyzed using logistic regression for a 2 × 2 factorial design with an interaction term. We analyzed H2 and H3 by testing with indicator variables for combined group membership, as described subsequently in more detail. We created unadjusted models and models that were adjusted for sex and education. Each hypothesis was examined by a complete case analysis (primary analysis) and 2 sensitivity analyses: penalty imputation, in which participants with missing outcomes were regarded as smoking, and multiple imputation of missing outcomes. For complete case and penalty imputation analyses, we report unadjusted and adjusted regression results accounting for unbalanced covariates introduced by peer recruitment. For multiple imputation, we stratified the imputation of missing outcome values by study groups and generated 100 imputation sets. The imputation model built on covariates that were unbalanced due to missing data or predictive for outcome values. The same covariates were used to adjust the analysis model.H1 comprised 3 subhypotheses. The first H1 subhypothesis compared participants exposed to the ML recommender and viral tool kit interventions (group A) vs those exposed only to the ML recommender intervention (group B). The second H1 subhypothesis compared participants in group A vs those who were exposed only to the viral tool kit and standard messaging (group C). The third H1 subhypothesis compared individuals in group A vs those who were exposed to standard messaging but not the viral tool kit (group D) (H2 compared 2 combined groups (individuals exposed to the ML recommender intervention regardless of exposure to the viral tool kit [A and B]) vs all others (C and D). This hypothesis also compared 2 additional combined groups (individuals exposed to the viral tool kit regardless of exposure to the ML recommender [A and C]) vs all others (B and D) (Although the number of nicotine tests was small, we examined test results for all hypotheses by categorizing tests by smoker vs nonsmoker groups and used the χ