Nominal data are one of the four levels of measurement described in 1946 by S. S. Stevens, a Harvard psychologist. The four levels are nominal, ordinal, ratio, and interval data, and all have specific definitions of their characteristics. It is important to identify the type of data being collected in a research study, so that the correct type of statistical analysis is performed. This entry describes the unique characteristics of nominal data and outlines the data analysis techniques permissible to use with these results.

Nominal data are considered the most crude or simplest of the four levels of measurement. Nominal data are also called categorical, labeled, or nonranked information because the value given functions only to delineate each individual result and to allow the researcher to ...