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Stanley Smith Stevens (November 4, 1906 – January 18, 1973) was an American psychologist who founded Harvard's Psycho-Acoustic Laboratory, studying psychoacoustics, and he is credited with the introduction of Stevens's power law. Stevens authored a milestone textbook, the 1400+ page Handbook of Experimental Psychology (1951). He was also one of the founding organizers of the Psychonomic Society. In 1946 he introduced a theory of levels of measurement widely used by scientists but whose use in some areas of statistics has been criticized. In addition, Stevens played a key role in the development of the use of operational definitions in psychology.A Review of General Psychology survey, published in 2002, ranked Stevens as the 52nd most cited psychologist of the 20th century. He was a member of the American Academy of Arts and Sciences, the United States National Academy of Sciences, and the American Philosophical Society.