Level of measurement or scale of measure is a classification that describes the nature of information within the numbers assigned to variables. The best known classification is that developed by the psychologist Stanley Smith Stevens, who proposed four levels, or scales, of measurement: nominal, ordinal, interval, and ratio. Other classifications include those by Chrisman and by Mosteller and Tukey. This framework of distinguishing levels of measurement originated in psychology and is widely criticized by scholars in other disciplines.