Term
Double-blind
Neither the participants nor the investigators know who is receiving which treatment.
Blinding protects a trial from expectations. Patients who know they received the real drug report differently; investigators who know assignments score outcomes and manage patients differently, usually without intending to. Double-blinding removes both channels; quadruple-blind extends the mask to outcome assessors and statisticians.
Open-label results, where everyone knows the assignment, are graded lower on this site for exactly this reason: the design cannot separate the drug's effect from the effect of knowing about the drug, and subjective endpoints inflate under that knowledge.
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