control group n.
In experimental design, a comparison group of research participants or subjects who, when the independent variable is manipulated, are not exposed to the treatment that subjects in the experimental group are exposed to, but who in other respects are treated identically to the experimental group, to provide a baseline against which to evaluate the effects of the treatment. The first deliberate use of a control group was described in the ‘Statistical Inquiries into the Efficacy of Prayer’ by the English explorer, amateur scientist, and psychologist Sir Francis Galton (1822–1911), published in Fortnightly Review in 1872. Galton explained the idea as follows: ‘We simply look for the final result—whether those who pray attain their objectives more frequently than those who do not pray, but who live in all other respects under similar conditions’ (p. 126). His results suggested that prayer is ineffective. Compare experimental group.