What Is a Placebo?

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A placebo is a procedure or substance with no inherent medicinal value. Placebos are often used in statistical experiments, especially those involving pharmaceutical testing, in order to control the experiment as much as possible. We will examine the structure of experiments and see the reasons for using a placebo.


Experiments typically involve two different groups: an experimental group and a control group.

The members of the control group do not receive the experimental treatment and the experimental group does. In this way, we are able to compare the responses of members in both groups. Any differences that we observe in the two groups may be due to the experimental treatment. But how can we be sure? How do we really know if an observed difference in a response variable is the result of an experimental treatment?

These questions address the presence of lurking variables. These kinds of variables influence the response variable but are often hidden. When dealing with experiments involving human subjects we should always be on the lookout for lurking variables. A careful design of our experiment will limit the effects of lurking variables. Placebos are one way to do this.

Use of Placebos

Humans can be difficult to work with as subjects for an experiment. The knowledge that one is a subject of an experiment and a member of a control group can affect certain responses.

The act of receiving a medication from a doctor or nurse has a powerful psychological effect on some individuals. When someone thinks they are being given something that will produce a certain response, sometimes they will exhibit this response. Because of this, sometimes doctors will prescribe placeboes with therapeutic intent, and they can be effective treatments for some issues.


To mitigate any psychological effects of the subjects, a placebo can be given to the members of the control group. In this way, every subject of the experiment, in both the control and experimental groups, will have a similar experience of receiving what they think is medication from a health professional. This also has the added benefit of not revealing to the subject if he or she is in the experimental or control group.

Types of Placebos

A placebo is designed to be as close to the means of administration of the experimental treatment as possible. Thus placebos can take on a variety of forms. In the testing of a new pharmaceutical drug, a placebo might be a capsule with an inert substance. This substance would be chosen to have no medicinal value and is sometimes referred to as a sugar pill.

It is important that the placebo mimic the experimental treatment as closely as possible. This controls the experiment by providing a common experience for everyone, no matter which group they are in. If a surgical procedure is the treatment for the experimental group, then a placebo for the members of the control group could take the form of a faked surgery. The subject would go through all of the preparation and believe that he or she was operated on, without the surgical procedure actually being performed.