What is Party Identification?

Legal Definition
Party identification refers to the political party with which an individual identifies. Party identification is loyalty to a political party. Party identification is typically determined by the political party that an individual most commonly supports (by voting or other means).

Some researchers view party identification as "a form of social identity", in the same way that a person identifies with a religious or ethnic group. This identity develops early in a person's life mainly through family and social influences. This description would make party identification a stable perspective, which develops as a consequence of personal, family, social and environmental factors. Other researchers consider party identification to be more flexible and more of a conscious choice. They see it as a position and a choice based on the continued assessment of the political, economic and social environment. Party identification can increase or even shift by motivating events or conditions in the country.

Party identification has been most studied in the United States. In other countries party identification has often been considered a subset of other levels of identity such as class, religion, or language; or to vary rapidly over time.

A number of studies have found that a partisan lens affects how a person perceives the world. Partisan voters judge character flaws more harshly in rival candidates than their own, believe the economy is doing better if their own side is in power, and underplay scandals and failures of their own side.
-- Wikipedia