Statistical Analysis
Under the assumption of an average 20% PSA positivity rate at each follow-up time point, and accounting for 20% correlation between repeated measures and type 1 error rate adjustment due to multiple comparisons between randomized groups, our a priori assessment suggested that a sample size of 450 (150 per group) would provide > 90% power to detect a 15% difference in PSA detection between randomized groups. To investigate differences in the frequency of condomless vaginal sex between randomized contraceptive groups, we calculated the frequency of PSA detection at the month six and final study visits. We then compared the proportion of PSA positive specimens by randomized contraceptive group at the month six and final visits separately using the Cochran–Mantel–Haenszel test stratified by study site with Bonferroni correction. We used a generalized logistic growth curve model adjusting for site, age (continuous) and specimen collection order to evaluate whether the proportion of PSA positive specimens differed significantly by randomized group and/or over time. We evaluated the concordance of self-reported sexual behaviour data and PSA detection in two ways by randomized study group: (1) the proportion of women who reported no vaginal sex, or only condom-protected vaginal sex in the past seven days, who had detectable PSA, and (2) the proportion of women who reported their last vaginal sex act to have been within 3 days with a condom, or reported their last vaginal sex act to have been ≥ 4 days ago whether or not they report condom use during that last act, who had detectable PSA. Using these data, we estimated the proportion of potential misreporting, and associated 95% confidence interval, overall and by randomized contraceptive group at the month 6 and final visits individually and jointly. The same statistical analysis approaches described above were used to compare potential misreporting by randomized contraceptive method and to evaluate whether the proportion of potential misreporting differed by group and over time. All data analyses were conducted using SAS version 9.4 (Cary, NC, USA).