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External Control Arm

Meaning

An External Control Arm (ECA) in a clinical trial refers to a cohort of patients whose outcome data is systematically collected from sources outside the concurrently run randomized study, often derived from historical trials, patient registries, or robust real-world data sources. This design element is occasionally utilized in hormonal research, particularly for rare conditions or when a traditional, concurrently enrolled placebo arm is ethically challenging, allowing all current trial participants to receive the active hormonal intervention. Careful statistical adjustments are necessary to account for potential confounding differences between the external and interventional cohorts.