The definition of an "independent voter" is controversial and fraught with implications.
The earliest concept of independents is of a person whose political choices, by definition, were made based on issues and candidates (due to lack of party affiliation). Furthermore, early studies of voting behavior conclusively demonstrated that self-identified independent voters are less interested in specific elections than partisan voters, poorly informed about issues and candidates, and less active politically. However, a contrary view emerged: The independent usually voted on the basis of deeply ingrained beliefs, attitudes and loyalties, and is more like the strongly partisan voter than any other voter (or the idealized "independent").
By the 1960s, scholars attempted to define the independent based on behavior, rather than party identification or loyalty. Focusing on ticket splitters, these studies depicted an independent voter who had the same level of political interest as strong partisans and who voted largely based on the issues with which they strongly agreed and/or disagreed. However, by focusing on voting behavior, this definition of the independent ignored non-voters. Critics claimed that the independent voter is merely a subset of the larger set of independents, which should also include non-voters. Studies also found that voting and not-voting is deeply affected by the particular candidate running in an election. Voting, therefore, is more reflective of what candidate is running—and therefore a poor measure of partisanship.
More recently, scholars focused on self-identification as a good measure of a person's political independence. The value of self-identification as a measure of a person's political independence or partisanship is that it is seen as a proxy for the behavior which should be exhibited by the independent voter. Additionally, self-identification could be easily captured either with a nominal question ("Do you self-identify with an existing political party?", a question which is answered with a "yes" or a "no"), or by a structured ordinal question ("Generally speaking, do you consider yourself a Democrat, a Republican, an independent, or what?"). The first analyses of this measure of political independence found that there were significant differences between those individuals who self-identified as "independent" and those who listed "no preference" as to party identification. Individuals who expressed "no preference" usually exhibited low levels of interest in politics, low levels of knowledge about the candidates and issues, low frequency of voting, and less confidence in their ability to influence politics.
Although some scholars continue to conclude that self-description is the best measure of partisanship or independence, a number of studies have found debilitating problems with this measure. The nature of the voter registration system and the appearance of the ballot, the way the question reinforces a unidimensional interpretation of the political arena, the measure's failure to function in a multi-party political system, the measure's confusion of the theoretical relationship between partisanship and the intent to vote, question wording errors which confuse a social group with a political party, failure to predict policy (versus candidate) preferences, question order, and failure to measure partisanship accurately when there are sizeable differences in party size all confound accurate measurement of partisanship and independence using this measure. Even the nature of a survey instrument as a measure of partisanship and independence has been called into question.
There are several synonyms for the term independent voter. In the U.S. state of