Fig. 2From: Pay-it-forward gonorrhea and chlamydia testing among men who have sex with men in China: a study protocol for a three-arm cluster randomized controlled trialSchematic of cluster randomization procedure and sample allocation. This schematic diagram illustrates the cluster randomization procedure, average volume of testers who visit the study site for HIV tests during a typical week, and allocation. There are 30 clusters and 300 total participants, which satisfy the sample size. The sequence shown is for illustration and is not the actual allocation sequenceBack to article page