Cluster randomized trials are performed when an intervention must be delivered to a group of patients like when testing new nursing protocols on award or different means for cleaning beds on a ward. One type of cluster trials is called a stepped-wedge where every cluster in the study ultimately undergoes the intervention. How this works it is explained by Susan Ellenberg, PhD, from the Department of Biostatistics, Epidemiology, and Informatics at the University of Pennsylvania School of Medicine. Related Article: The Stepped-Wedge Clinical Trial