Balancing the Number and Size of Sites: An Economic Approach to the Optimal Design of Cluster Samples

The design of randomised controlled trials (RCTs) entails decisions that have economic, as well as statistical implications. In particular, the choice of an individual or cluster randomisation design may affect the cost of achieving the desired level of power, other things equal. Furthermore, if cluster randomisation is chosen, the researcher must decide how to balance the number of clusters, or "sites", and the size of each site. This paper investigates these interrelated statistical and economic issues. Its principal purpose is to elucidate the statistical and economic trade-offs to assist researchers to employ RCT designs that have desired economic, as well as statistical, properties.