Cluster Randomized Trials

Over the last century, the randomized clinical trial has become the gold standard for interventional studies. Typically individuals are randomly assigned to an experimental group or a control group. What if it was impractical or unethical to randomize individuals to a treatment group? This is where the cluster randomized trial design comes in. Cluster randomized trials randomize groups, rather than individual subjects, to receive different interventions. For example, in this issue one such trial examined the effect of hand hygiene on influenza infection rates and absenteeism in elementary schools in Cairo, Egypt.

Since it is difficult to have each student in a school gain exposure to different hand hygiene practices without some overlap between the individuals, …