Randomized controlled trial

A randomized controlled trial or RCT is a clinical treatment trial with at least two treatment groups, one receives the treatment being tested and the other group receives a placebo, sham therapy or alternative treatment. Participants are allocated to a treatment group randomly rather than being able to choose whether to undergo the treatment being tested or the alternative.

Types
This is particularly important when a trial's success is measured by subjective outcomes like participant or clinician questionnaires rather than independent measurable outcomes like employment rates, physiological measures (e.g., distance walked, heart rate, muscle strength, blood test results, hospital admissions).
 * Unblinded: participants know whether the treatment is a placebo / sham or the one being tested, which introduces possible bias.


 * Blinded (single blinded): participants do not know whether the treatment is a placebo / sham or the one being tested, but the researchers / clinicians delivering or assessing the treatment do know. Bias from clinicians may affect results, and may have an effect on patient reports, e.g., positive or negative clinician feedback, and clinician encouragement.


 * Double-blinded: participants and clinicians / researchers do not know whether the treatment is a placebo / sham or the one being tested, the researcher analyzing the trial data is also not aware which group received which intervention.

Limitations
Double-blinded studies are typical in medication trials because it is easy to provide placebo medications that look like the intervention being tested.

For some type of treatments, it may not be possible to blind participants to the intervention, for example in psychotherapy, counseling, or behavioral treatments such as cognitive behavioral therapy or graded exercise therapy.