Group allocation

The group allocation study design, also known as a cluster-randomized trial (CRT), randomizes groups of study participants as a single unit. Although not a traditional study design, the prevalence of this type of randomized trial has been steadily increasing in the past decade. Most notably, this design has established an important role in studying interventions that are delivered at the systems level. A major advantage of this design is that it avoids contamination of the intervention within clusters. In addition, there are some pitfalls, such as allocation bias and aspects of the statistical analysis, that researchers need to consider in designing and executing a CRT. Variations of the CRT design exist, such as the stepped-wedge design, that address certain limitations. Ultimately, this study design may be the optimal approach to investigate interventions such as quality improvement or public health campaigns.