Median voter theory

The median voter theory, also known as the median voter theorem and the median voter model, is a famous voting model positing that "in a majority election", if voter policy preferences can be represented as a points along a single dimension, if all voters vote deterministically for the politician that "commits" to a policy position closest to their own preference, and if there are only two politicians, then if the politicians want to maximize their number of votes they should both commit to the policy position preferred by the median voter. This strategy is a Nash equilibrium. It results in voters being indifferent between candidates and casting their votes for either candidate with equal probability. Hence in expectation each politician receives half of the votes. If either candidate deviates to commit to a different policy position, the deviating candidate receives less than half the vote.

Political commentator Mickey Kaus of "Slate Magazine" [http://www.slate.com/id/2073262/ wrote] in 2004 that the United States presidential elections of 2000 and 2004, in addition to local elections in those years, provide evidence that this phenomenon is taking place in the United States.

The theorem was first articulated in Duncan Black's 1948 article, "On the Rationale of Group Decision-making" and popularized by Anthony Downs's 1957 book, "An Economic Theory of Democracy".

Necessary Conditions

There are many instances in which the Median Voter Theorem may not be applied. Among the most common is the case of preferences which are not single-peaked (multimodal preferences). If several voters are voting on the budget of a public school, for instance, and there are three options: low, medium and high. If one of them prefers both low and high to medium, then the preferences will not be single-peaked (they form a "valley", instead of a "mountain" if represented in an unidimensional diagram).

The non-verification of single-peaked preferences may lead to the majority cycle trap, in which the agenda-maker who chooses in which order propositions are voted, may have the power to choose any outcome.

Applied

* [http://www.louisville.edu/~bmhawo01/econpage/342/handouts/median_voter_theorem/mvt_q2.html simple example]
* [http://www.daviddfriedman.com/Academic/Price_Theory/PThy_Chapter_19/PThy_Chap_19.html to tariffs]
* [http://www.nber.org/papers/W11972 to local private goods]

References

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* Congleton, Roger (2002). [http://rdc1.net/forthcoming/medianvt.pdf The Median Voter Model] . In * cite book | author=C. K. Rowley (Ed.); F. Schneider (Ed.)| title=The Encyclopedia of Public Choice | publisher=Kluwer Academic Press | year=2003 | ISBN=?