This document discusses the four scales of measurement used in statistics: nominal, ordinal, interval, and ratio. Nominal scales simply categorize variables without order, like gender or favorite color. Ordinal scales maintain unique identities and a rank order, but not necessarily equal distances, like the results of a horse race. Interval scales preserve equal distances between units in addition to identity and order, as in the Fahrenheit temperature scale. Ratio scales satisfy all properties by also having a true zero point, such as weight scales.