Level of measurement or scale of measure is a classification that describes the nature of information within the values assigned to variables.[1] Psychologist Stanley Smith Stevens developed the best-known classification with four levels, or scales, of measurement: nominal, ordinal, interval, and ratio.[1][2] This framework of distinguishing levels of measurement originated in psychology and has since had a complex history, being adopted and extended in some disciplines and by some scholars, and criticized or rejected by others.[3] Other classifications include those by Mosteller and Tukey,[4] and by Chrisman.[5]