The 1946 article by Stanley Smith Stevens titled “On the Theory of Scales of Measurement” defined measurement as the assignment of numerals to objects or events according to rules. Stevens [Page 972]went on to discuss how different rules for assigning such numbers resulted in different types of scales. In the remainder of the article, Stevens elaborated on four such scales in terms of the mathematical transformations that can be conducted without changing their properties and the statistical operations that he considered permissible for each. Stevens's definition of measurement and the four levels of measurement he described have since become iconic in social science measurement.

The four scales of measurement specified by Stevens were the nominal, ordinal, interval, and ratio scales. The scales form a specific hierarchy ...