Statistics Dictionary

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In an experiment, subjects respond differently after they receive a treatment, even if the treatment is neutral. A neutral treatment that has no "real" effect on the dependent variable is called a placebo, and a subject's positive response to a placebo is called the placebo effect.

To control for the placebo effect, researchers often administer a neutral treatment (i.e., a placebo) to the control group. The classic example is using a sugar pill in drug research. The drug is effective only if subjects who receive the drug have better outcomes than subject who receive the sugar pill.

See also:   Experiments