crtrest: A command for ratio estimators of intervention effects on event rates in cluster randomized trials

We describe five asymptotically unbiased estimators of intervention effects on event rates in nonmatched and matched-pair cluster randomized trials, and we present a bias-corrected version of the estimators for use when the number of clusters is small. The estimators are the ratio of mean counts ( r 1), ratio of mean cluster-level event rates ( r 2), ratio of event rates ( r 3), double ratio of counts ( r 4), and double ratio of event rates ( r 5). r 1, r 2, and r 3 estimate the total effect, which comprises the direct and indirect effects; r 4 and r 5 estimate the direct effect. We describe a new command, crtrest, that provides these ratio estimators and their standard errors in nonmatched and matched-pair cluster randomized trials.