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.
In the 1950s the Michigan Model described in The American Voter rose to prominence. It argued that partisan identity formed early in life and would rarely change, with the rare exception of Realignment elections. Voting behaviour and political opinions would grow out of this partisanship. The theory worked well to explain why party structures remained stable in most democracies for the first part of the 20th century.
In the 1980s a revisionist school developed along with the breakdown of the two-party system and growing dealignment in several major democracies. It argued that partisan identity formed slowly in a Bayesian process as voters accumulate data and opinions over a lifetime. By late in life, a single new piece of information will have little effect, but there is always the opportunity for partisan identity to change and will fluctuate based on short-term events for many voters.