Somewhat similar to a control condition, a placebo is used to determine whether an effect of a substance (or treatment) was indeed caused by that specific treatment. A placebo is a similar looking but ineffectual procedure (e.g., a similar looking and tasting pill). The difference between a placebo condition and treatment condition informs about the specific effect of the treatment. Placebos are used to rule out that an effect is merely driven by expectancy effects of the recipient.
defined by Jan Alexander Häusser