Sample size calculations
Sample size calculations are performed based on previous ITN durability data from Benin. For cohort 1, a sample size of 750 nets of each brand from 250 randomly selected households (assuming ~ 3 ITNs are distributed per household) in 5 study clusters was found sufficient to detect a 9.4% absolute difference (hazard ratio = 0.87) in ITN attrition rate assuming an attrition rate in the control arm of 70% over the 3 years and an intra-cluster correlation coefficient of 0.03. For cohort 2, a total of 522 ITNs will need to be withdrawn over three years and assuming a loss rate of 70% a total of 1800 ITNs will be marked per study arm at baseline. To reduce the impact of the durability study on the outcomes of the cRCT, cohort 2 nets will be obtained from households in the buffer areas of the selected clusters to exclude the core areas used for the cRCT sampling.For each experimental hut trial and at each timepoint, data on the number of mosquitoes per night and the magnitude of the different random effects (huts, sleepers, nights and observational error) will be reviewed after the first round of 9 or 13 weeks and power calculations conducted by simulation using previously described methods [