Cluster-Randomize Trials in Emergency Care Research

Objective Cluster-randomized trials (also called group-randomized trials) are increasingly common in emergency care research. In such trials, groups of participants are allocated to different interventions based on naturally occurring “clusters,” such as clinics, hospitals, or emergency medical services agencies. In this methodological review, we introduced key terminology and features of cluster-randomized trials, described common rationales for cluster-randomization and its most common limitations, and offered brief advice for conducting and critically appraising cluster-randomized trials in emergency care research. Results Researchers elect to use cluster-randomization when individual participant randomization is not preferred or not possible. Common reasons include a desire to limit contamination between study groups, logistical convenience relating to trial administration or study procedures, or the use of an intervention that is naturally group-oriented, such as an educational intervention or clinical decision support tool that is directed toward influencing clinician behaviors. Although cluster-randomization has advantages in these contexts, this approach also comes with some notable weaknesses, such as inflated sample size requirements, greater difficulty in blinding participants and researchers, and an increased risk of baseline imbalances between comparator groups. When reading and critically appraising cluster-randomized trials, emergency clinicians should consider whether researchers have appropriately justified group over individual randomization, accounted for different levels of clustering and the degree of correlation between participants within clusters (intracluster correlation), and appropriately consented various levels of participants to study participation. Conclusions Cluster-randomized trials are frequently used in emergency care research, especially as researchers are increasingly evaluating educational or electronic health record interventions that are naturally group-oriented or have a high risk of contamination. After reading this review, emergency medicine clinicians and researchers will have a foundational understanding of key cluster trial features and will be able to assess the quality and limitations of emerging evidence.