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

Abstract

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.