The process of preventing researchers and subjects participating in an experimental study from gaining knowledge of their treatment status.

• In a "single-blind" experimental study, the study subjects are unaware of their treatment assignment.
• In a "double-blind" experimental study, both the study subjects and the investigators monitoring the effects of the treatment are unaware of the treatment assignment
• In a "triple-blind" experimental study, the study subjects, the investigators administering the treatment, and the investigators monitoring the effects of the treatment are unaware of the treatment assignment.

Source: Aschengrau & Seage, p.184; Rothman and Greenland, p.69