A method of investigation in which neither the subject nor the investigator knows what treatment the subject is receiving.
A method of studying a drug, or other medical procedure in which both subjects and investigators are kept unaware of (blind to) who is actually getting which specific treatment. The method is one of the few ways of eliminating bias, conscious or unconscious, in both subjects and investigators. Classically, in drug studies the method involves the use of a look-alike placebo. In “triple blind” studies the people analyzing the data are also unaware of the treatment used.