What Counts as an Experiment?: A Transdisciplinary Analysis of Textbooks, 1930-1970

The textbook definition of experiment as manipulation of an independent variable while holding all other variables constant is generally treated as transdisciplinary and transhistorical. We examined the rise of this definition in psychology and other disciplines by comparing 236 introductory texts from psychology, sociology, biology, and physics published during the 1930s, 1950s, and 1970s. The definition of experiment in psychology texts did not approach uniformity until the 1970s and was not borrowed from texts of other disciplines. The standard definition is relatively absent from physics, infrequent in biology, and appears in sociology after its development in psychology. We discuss the enshrinement of experimentation as the sole method for the discovery of causes.