Levels of Measurement

Description

Four levels of measurement first crystallized by Stevens (1946) are generally recognized, though with some debate:

• 1. Nominal or categorical – in which individuals are placed in an exclusive category according to one or more characteristics;

• 2. Ordinal – individuals are ranked on a single criterion, such as their height (from the shortest to the tallest but without their actual height being recorded);

• 3. Interval – the distance between each pair of individuals is recorded on a continuous scale (such as weight in kilograms); and

• 4. Ratio – the nature of one individual is expressed as a ratio of another on the same intervally measured characteristic (such as individual a is twice the weight of b).

Thus, for example, on a nominal scale New York City contains eight million people and Los Angeles four million; on an ordinal scale, New York is larger than Los Angeles; on an interval scale New York has four million more residents than Los Angeles; and on a ratio scale New York is...