Placebo effect.

The term “placebo” is derived from a Latin term meaning “I shall please,” but it has come to mean a false substance. A placebo is generally given to the control group in a scientific experiment while the independent variable (item being tested) is given to other experimental groups. The placebo effect is the response of the control group, any changes in behavior—usually measurable, observable, or reported improvements in behavior or health—brought about as a result of exposure to this false substance. Using a placebo controls for the expectations of the subjects, in that neither the experimental subjects nor the control subjects know what to expect. If the subjects do not know whether they are in the experimental or control group but the experimenter does, this is known as a single-blind study. If neither the subjects nor the experimenter knows which group is the experimental one and which is the control, this is known as a double-blind study. A controls for both experimenter bias and subject expectations.