Stevens and the Operational Definition of Measurement in Psychology, 1935–1950

Chapter 8 broadens the narrative beyond utility measurement and discusses an important outcome of the 1930s British controversy over psychological measurement, namely the operational definition of measurement put forward by American psychologist Stanley Smith Stevens in 1946. For Stevens, measurement consists of the assignment of numbers to objects according to certain rules. Since there are various rules for assigning numbers to objects, there are various forms, or scales, of measurement. Each scale is identified by the empirical operations used to create it and by the class of mathematical transformations the numbers in each scale can be subjected to. From this operational viewpoint, unit-based measurement is just a particular, and quite restrictive, form of measurement. Stevens’s definition of measurement was broad enough to include the psychologists’ quantification practices as measurement and quickly became canonical in psychology. The final section of the chapter discusses drawbacks to Stevens’s operational theory of measurement.