Sample size
This study was designed to have 80% power to detect a 0.4 reduction in odds of intervention group reporting of RC in the past six months (equivalent to an 8-percentage point decrease) assuming a baseline prevalence of RC of 17%, cluster coefficient of variation of 0.5, inter-class correlation of <0.1%, and retention at three- and six-month follow-up visits of 85% and 75%, respectively, based on ARCHES studies completed in the United States.