Double-Blind: Typically used in Randomized Controlled Trials (RCTs). An experimental method in which both the patients and the research staff do not know and cannot figure out which patients are receiving treatment and which placebo.

Randomized Controlled Trial (RCT): A true experiment, in which the researcher randomly assigns some patients to at least one maneuver (treatment) and other patients to a placebo, or usual treatment. Key features = the classic way to evaluate effectiveness of drugs (or exercise, diet, counseling). Patients are followed over time (Prospective). If properly done, an RCT can be used to determine cause and effect.

From Evidence-Based Medicine Glossary: http://www.musc.edu/muscid/glossary.html