The group in a trial that the intervention is measured against.
The comparator arm (also called the control or reference arm) is the study group receiving a different treatment, a placebo, usual care, or no intervention, against which the experimental arm's outcomes are compared. The choice of comparator determines what a trial can actually claim: a placebo comparator supports efficacy claims, while an active-treatment comparator supports comparative or non-inferiority claims. Clinicians should check what the comparator actually was, since a weak or unrepresentative comparator can inflate apparent benefit.
This guide was auto-drafted and is pending editorial review.