Sample size
HIV and 0.4
DECAY
Data from our previous studies and the demographic surveillance suggested 8% of young people aged 15–30 have a transmissible HIV viral load (primary outcome 1), and around 35% are aware of their HIV status and either on PrEP or on ART with undetectable viral load (primary outcome 2). Our original design specified 2000 young people aged 15–30 (50 per cluster) interviewed in each of the three cross-sectional survey waves. Assuming an intracluster correlation coefficient (ICC) within wave of 0.1 for transmissible HIV and 0.4 for intervention uptake, and a decay (autocorrelation) between waves of 0.9 for both outcomes, this design provided 90% power to detect an increase from 35 to 47% in primary outcome 2 and 80% power to show a reduction in primary outcome 1 from 8 to 4% when comparing the intervention to standard of care [