Data analysis
REGRESSION, SECONDARY
Descriptive and bivariate (2-tailed independent t-tests; chi-square or Fisher’s Exact tests) statistics were used to compare baseline sample characteristics of index and alter participants in the control versus intervention arms, in separate analyses. To examine intervention effects on index and alter measures of CC-related processes, we conducted multiple linear regression analyses. In each model, the month 6 measure of the outcome was the dependent variable, while independent variables included the baseline measure of the dependent variable and an indicator of study arm. If a measure was missing at month 6, the baseline measure of the variable was used to replace the missing value. Normal probability plots were constructed for each dependent variable and examined qualitatively for violation of normality. Similar multiple logistic regression models were run to examine whether alter uptake of CC screening by month 6 was associated with the index and alter measures of CC-related processes.Measures of index and alter CC-related processes (potential mediators) were examined as mediators of the intervention effect on alter uptake of CC screening if the measure was significantly associated with both the intervention and alter CC screening. To test for mediation, we employed Proc Causalmed (SAS v9.4), which uses bootstrap resampling to compute standard errors and confidence intervals for causal mediation effects and decompositions. A two-step approach was used to test each potential mediator separately. In step one, the dependent variable was alter uptake of CC screening by month 6, while independent variables consisted of an indicator of study arm and the baseline measure of the mediator. In step two, the month 6 measure of the mediator was added to the model, resulting in the model assessing the mediating effect of change in the mediator from baseline to month 6. Covariates included in each model consisted of age < 35 years, any secondary education, and presence of a main sex partner. We examined each potential mediator separately, because the mediators are conceptually inter-correlated, and testing multiple mediators simultaneously would complicate the interpretation of the models. To test for moderation of the intervention effect on alter CC screening, for each potential moderator we ran a logistic regression modeling alter CC screening at month 6 as the dependent variable. Independent variables included an indicator for study arm, the moderator measured at baseline, and their interaction.