Cluster Randomized Trials: Lessons for Inflammatory Bowel Disease Trials

J Crohns Colitis. 2021 Aug 14;jjab149. doi: 10.1093/ecco-jcc/jjab149. Online ahead of print.

Bénédicte Caron 1Ferdinando D'Amico 2 3Silvio Danese 2 3Laurent Peyrin-Biroulet 1


Author information

  • 1Department of Gastroenterology and Inserm NGERE U1256, Nancy University Hospital, University of Lorraine, 54500 Vandoeuvre-lès-Nancy, France.
  • 2Department of Biomedical Sciences, Humanitas University, Pieve Emanuele, 20090 Milan, Italy.
  • 3IBD Center, Humanitas Research Hospital, IRCCS, Rozzano, 20089 Milan, Italy.


Randomized clinical trials are the gold standard for new drugs development. Clinical trials became 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 special attention in cluster randomized trials is the risk for imbalance of covariates at baseline which decreases 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 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.

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