Definition Level of measurement

In statistics, depending on the kind of data we ascertain, we use different kinds of scales. Not every attribute or variable can be translated to numerical values in the same way. Whereas body size can easily be depicted in centimeters or in feet and inches, this is not possible for variables, such as gender, and possible but difficult for levels of personal satisfaction.

The level of measurement expresses how quantifiable a value actually is, i.e., to what extent we can apply mathematical operations. We distinguish between four levels of measurement: nominal scales (non-metric or categorical), ordinal scales (non-metric or categorical), interval scales (metric), and ratio scales (metric). The nominal scale offers the least statistical information content, the ratio scale the most. Nominal and ordinal are non-metric or categorical scales, that is, their response values are not directly usable as a numerical value.Interval and ratio scales are metric scales that allow for various arithmetic operations.

Examples of nominal scales include gender (male, female) and color (blue, yellow, red, green, etc.).

Examples of ordinal scales include type of residence (single house, village, town, city) and category of vehicle (compact car, medium-sized vehicle, luxury car, etc.). 

Examples of interval scales include the temperature in degrees Celsius and the IQ scale. 

Examples of ratio scales include body height and monthly income.