Cluster Randomized Trials: Lessons for Inflammatory Bowel Disease Trials

Randomized clinical trials are the gold standard for the development of new drugs. Clinical trials have become increasingly complex, in particular in the field of inflammatory bowel diseases. For this reason, a new study design called ‘cluster randomized trial’ has been introduced. Cluster randomized trials randomly assign groups of individuals within a population of interest, such as people in a particular research site, clinic or hospital, and measure the effects of an intervention at the individual level. In contrast to individual randomization, cluster randomization permits the evaluation of a cluster-level intervention, may be logistically simpler and less expensive than a conventional randomized trial, and can help reduce the effect of treatment contamination. An important aspect requiring particular attention in cluster randomized trials is the risk for imbalance of covariates at baseline which decreases the statistical power and precision of the results, and reduces face validity and credibility of the trial results. A variety of restricted randomization methods have been proposed to minimize risk of imbalance. Our aim here is to clarify the advantages and drawbacks of cluster randomized trials in order to properly interpret study results and to identify their role in upcoming inflammatory bowel disease trials.