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I would like to thank the author for this well written and generally clear explanation of sample size calculations for cluster randomised trials. However, I stumbled across the following statement:
" An intracluster correlation coefficient (ICC) of 1 would mean that there was no correlation of the primary outcome between patients within a cluster and all the variation was a result of variation between clusters."
It seems that the phrase "no correlation [...] between patients within a cluster" in the above sentence should either be replaced by "no variation [...] between patients within a cluster" or by "perfect correlation [...] between patients within a cluster". For the ICC to be 1, all subjects would have to have the same outcome of interest, implying that if there was variation, it would be entirely due to variation between clusters.