Placebo-controlled study

Placebo-controlled studies are a way of testing a medical therapy in which, in addition to a group of subjects that receives the treatment to be evaluated, a separate <a href="/facts/Scientific_control/FXHfQwHx">control</a> group receives a sham "<a href="/facts/Placebo/3fw50t53">placebo</a>" treatment which is specifically designed to have no real effect. Placebos are most commonly used in <a href="/facts/Blind_experiment/6ALSxX8M">blinded</a> trials, where subjects do not know whether they are receiving real or placebo treatment. Often, there is also a further "natural history" group that does not receive any treatment at all.
The purpose of the placebo group is to account for the <a href="/facts/Placebo_effect/3fw50t53">placebo effect</a>, that is, effects from treatment that do not depend on the treatment itself. Such factors include knowing one is receiving a treatment, attention from health care professionals, and the expectations of a treatment's effectiveness by those running the research study. Without a placebo group to compare against, it is not possible to know whether the treatment itself had any effect.
Patients frequently show improvement even when given a sham or "fake" treatment. Such intentionally inert <a href="/facts/Placebo/3fw50t53">placebo</a> treatments can take many forms, such as a pill containing only sugar, or a medical device (such as an <a href="/facts/Medical_ultrasonography/Ju5BFuuV">ultrasound machine</a>) that is not actually turned on. Also, due to the body's natural healing ability and statistical effects such as <a href="/facts/Regression_to_the_mean/l7hDWAVR">regression to the mean</a>, many patients will get better even when given no treatment at all. Thus, the relevant question when assessing a treatment is not "does the treatment work?" but "does the treatment work better than a placebo treatment, or no treatment at all?" More broadly, the aim of a clinical trial is to determine what treatments, delivered in what circumstances, to which patients, in what conditions, are the most effective.
Therefore, the use of placebos is a standard <a href="/facts/Scientific_control/FXHfQwHx">control</a> component of most clinical trials, which attempt to make some sort of <a href="/facts/Quantitative_property/C1t5h075">quantitative</a> assessment of the efficacy of medicinal drugs or treatments. Such a test or clinical trial is called a placebo-controlled study, and its control is of the <a href="/facts/Scientific_control/FXHfQwHx">negative</a> type. A study whose control is a previously tested treatment, rather than no treatment, is called a positive-control study, because its control is of the <a href="/facts/Scientific_control/FXHfQwHx">positive</a> type.
This close association of placebo effects with RCTs has a profound impact on how placebo effects are understood and valued in the scientific community.

Placebo-controlled study open-in-new

Placebo-controlled study