Median Voter Theorem - Explanations

Explanations

To appreciate the logic of the median voter model, consider a setting where three individuals: Al, Bob and Charlie are to choose a restaurant to eat lunch at. Al prefers a restaurant where lunch can be had for $5.00, Bob favors a bit better fare at a restaurant serving $10.00 lunches, and Charlie wants a gourmet restaurant where lunch will cost around $20.00. Bob can be said to be the median voter because exactly the same number of individuals prefer a more expensive restaurant than Bob as prefer a less expensive restaurant than Bob, here one each. For convenience assume that, given any two options, each member of the lunch group prefers restaurants with prices closer to their preferred restaurant to ones that are farther from it. Now consider some majority decisions over alternative restaurants:

The weak form of the median voter theorem says the median voter always casts his or her vote for the policy that is adopted. Note that Bob always votes in favor of the outcome that wins the election. Note also Bob's preferred $10 restaurant will defeat any other. If there is a median voter, his (or her) preferred policy will beat any other alternative in a pairwise vote. (The median voter's ideal point is always a Condorcet winner.) Consequently, once the median voter's preferred outcome is reached, it cannot be defeated by another in a pairwise majoritarian election. The strong form of the median voter theorem says the median voter always gets his most preferred policy.

The median voter theorem seems to explain a few of the phenomena that occur in majoritarian voting systems. First, it may explain why politicians tend to adopt similar platforms and campaign rhetoric. In order to win the majority vote, politicians must tailor their platforms to the median voter. For example, in the United States, the Democratic and Republican candidates typically move their campaign platforms towards the middle during general elections campaigns. Just as sellers in the private market try to win over their competitor’s customers by making slight changes to better their products, so, too, do politicians deviate only slightly from their opponent’s platform so as to gain votes.

Second, the median voter theorem may explain why radical candidates or parties rarely get elected. If a politician is, for example, an extreme liberal on the very left end of the political spectrum, they will not capture nearly as many votes as the politician whose campaign platforms are more moderate. Finally, the theorem may explain why two major political parties tend to emerge in majoritarian voting systems (Duverger's law). Indeed, in the United States there are countless political parties, but only two major parties play a part in almost every major election: the Democratic and Republican parties. According to the median voter theorem third parties will rarely, if ever, win elections for the same reason why extreme candidates do not tend to win. The major parties tend to co-opt the platforms of the minor parties in order to secure more votes.