Using Economics to Explain Why Elections Are Decided by the Median Voter

Abstract：The economic explanation of why elections are decided by centrists stems from the "Median Voter Theorem," which posits that in a majority-vote system, candidates must appeal to the median voter to secure victory. Unlike markets where decisions align with average preferences, elections reflect the preferences of the median voter. Candidates strategically align policies to attract centrist voters, ensuring the broadest support. Historically rediscovered by Duncan Black in 1948 and popularised by Anthony Downs in 1957, this theory underscores how politicians often tailor ideologies to win elections rather than champion ideals. It highlights the crucial role of centrists in shaping electoral outcomes.

Elections are typically seen as political events, but how do they relate to economics? The connection is significant, as economists began studying elections long ago. Let’s start with a simple model.

1. Differences Between Market Transactions and Voting in Public Choice

Imagine three individuals deciding where to have lunch, each with different spending preferences:

• The first prefers a modest $5 meal; anything cheaper or more expensive is unappealing.

• The second believes $10 is ideal, disliking both cheaper and costlier options.

• The third prefers an extravagant $50 meal, with dissatisfaction increasing as the price diverges from $50.

This group represents a "single-peaked preference," where each person's ideal choice lies at a specific point, and satisfaction diminishes as options move away from it. How would they resolve this choice? Let’s first explore a market scenario.

In a market, decisions follow Coase's theorem: the highest bidder prevails. The third individual, valuing the meal most at $50, might pay the others to agree on a pricier lunch. For instance, the $5 and $10 proponents might settle for a $25 lunch if compensated for the higher cost. All parties benefit because the high spender gains more satisfaction than the extra cost incurred.

The market outcome averages preferences. In this case, the average of $5, $10, and $50—approximately $22—guides the decision. However, in elections, votes cannot be bought. How does the decision change?

Through voting, decisions reflect majority preferences. Here, the $5 voter represents the low end, the $50 voter the high end, and the $10 voter sits in the middle. The middle voter effectively decides the outcome because their preference aligns with the majority. The group will settle on a $10 meal—the median preference.

This contrast illustrates a key difference: markets produce outcomes based on averages, while elections are determined by medians.

2. Success in Elections Depends on Capturing the Median Voter

Economists extend this basic model to analyze political elections. Real-world elections involve diverse and complex policies, from wage laws and retirement ages to education reforms. Voters don’t decide on every policy individually but choose from limited “bundles” offered by parties or candidates.

Political parties, therefore, strive to appeal to the broadest possible base. Imagine a political spectrum from left to right. A candidate seeking victory must capture the median voter—the one whose position lies at the center of the spectrum.

Initially, if only one candidate runs, they can position themselves anywhere, knowing all voters will support them. However, when a second candidate enters, they will strategically position themselves close to the median voter, yet distinct enough to attract the other half of the electorate.

As more candidates join, each adjusts their position to maximize appeal to a broader voter base while maintaining distinguishable stances. Over time, this competition pulls all contenders closer to the median, as only those catering to median voter preferences can secure a majority.

This "median voter theorem" demonstrates that elections are decided by the preferences of the middle ground, compelling candidates to align their platforms accordingly.

3. The Rediscovery of the Median Voter Theorem

Although the median voter theorem was rediscovered in 1948 by economist Duncan Black, it was first proposed by a French mathematician in the 16th century. Black’s work laid the foundation for Anthony Downs’s 1957 classic, An Economic Theory of Democracy, which systematically applied economic principles to democratic elections. This work, later translated into Chinese, has been instrumental in reshaping political thought.

Prior to this, politics was often viewed as a contest of ideals—who had the noblest vision or the most inspiring goals. However, the median voter theorem turned this perception on its head. It showed that, regardless of personal ideals, politicians must appeal to the median voter’s preferences to win elections. This realization shifted the focus from lofty aspirations to pragmatic strategies tailored to electoral success.

In essence, the theorem reveals that political behavior is not purely ideological but deeply influenced by the need to secure votes. To win, politicians prioritize the preferences of the median voter, reshaping their platforms to align with the center. This insight underscores the power of the median voter in shaping electoral outcomes.