Nominal category

A nominal category or a nominal group is a group of objects or ideas that can be collectively grouped on the basis of shared, arbitrary characteristic.

Valid data operations

A nominal group only has members and non-members. That is, nothing more can be said about the members of the group other than they are part of the group. Nominal categories cannot be numerically organized or ranked. The members of a nominal group cannot be placed in sequential, ordinal or ratio orders.

Nominal categories of data are thus most commonly compared to ordinal and ratio data, to see if nominal categories play a role in determining these other factors. For example, the effect of race (nominal) on income (ratio). Nominal variables are seldom the variables being explained by the research.

Examples

For example citizenship is a nominal group. A person can be a citizen of a country, or he cannot. A citizen of Canada does not have "more citizenship" than a citizen of Australia; therefore it is impossible to order citizenship according to any sort of mathematical logic.