Term
Placebo-controlled
A trial design in which the comparison arm receives an inactive treatment that looks identical to the real one.
A placebo arm answers the question a single-arm study cannot: how much of the observed improvement would have happened anyway, through natural fluctuation, regression to the mean, extra clinical attention, or expectation. In diseases with strong placebo responses, that share can be large.
Where withholding treatment would be unethical, trials compare against an active drug or add the study drug on top of standard of care instead. The grading question stays the same: was there a concurrent control that isolates the drug's own effect?
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