Cluster Randomised Trial

A cluster randomised trial is a trial design in which randomisation is carried out by grouping areas, facilities, schools, etc., into a single unit (i.e. a cluster). It is used when adopting an individual randomised trial in which the intervention is allocated to individual subjects within the same cluster is impossible or inappropriate. Cluster randomised trials have specific issues that differ from individual randomised trials in terms of implementation and statistical methodology. In particular, about the statistical aspects, it is essential to consider intracluster correlation in sample size calculation and statistical analysis. In addition, although the basic design of cluster randomised trials is a parallel group, different trial designs (e.g., stepped wedge cluster randomised trials and cluster randomised crossover trials) may be adopted mainly from the perspective of practicality and efficiency. In this paper, we will explain the situations in which cluster randomised trials are applied, points to note, frequently used sample size calculation and statistical analysis methods, and derivative designs, with examples of their practical application in the medical field.