Math Problem Statement

Does the Pairwise Comparison Method (Copeland's Method) satisfy the Majority Condition? You should fully justify your answer either by giving a counterexample if it does not, or by giving a mathematical argument to show that it always does

Solution

To determine if Copeland's Method satisfies the Majority Condition, let's first clearly define both the method and the condition:

Majority Condition:

A voting method satisfies the Majority Condition if, whenever a candidate is preferred by a majority of voters over every other candidate in head-to-head (pairwise) comparisons, that candidate should be the winner.

Copeland's Method:

In Copeland’s Method, each candidate competes head-to-head against every other candidate. A candidate receives:

  • 1 point for winning a head-to-head comparison,
  • 0.5 points for a tie, and
  • 0 points for losing a head-to-head comparison.

The candidate with the most total points at the end wins the election.

Does Copeland's Method satisfy the Majority Condition?

Yes, Copeland's Method does satisfy the Majority Condition. Here's the reasoning:

Justification:

  1. If a candidate AA satisfies the Majority Condition, this means that candidate AA beats every other candidate in pairwise head-to-head comparisons.
  2. In each of these pairwise comparisons, AA wins and therefore earns 1 point per comparison. Suppose there are nn candidates. Then AA competes against n1n - 1 other candidates, earning 11 point per comparison.
  3. The total score for AA is then n1n - 1, the maximum score any candidate can achieve.
  4. No other candidate can get a score higher than AA because AA has won every comparison. Therefore, candidate AA must have the highest score overall.
  5. As a result, AA, the candidate satisfying the Majority Condition, will be declared the winner under Copeland's Method.

Conclusion:

Because a candidate who is preferred by the majority in every head-to-head comparison will accumulate the maximum possible score, Copeland's Method satisfies the Majority Condition.

Would you like further details or have any questions? Here are some related questions to consider:

  1. What other voting methods satisfy the Majority Condition?
  2. Does Copeland's Method satisfy other fairness criteria like Condorcet or Monotonicity?
  3. Can a tie occur under Copeland's Method? How are ties resolved?
  4. What are the weaknesses of Copeland's Method compared to other Condorcet methods?
  5. How does the Majority Condition relate to Arrow's Impossibility Theorem?

Tip: Understanding how different voting methods satisfy or fail to satisfy various fairness criteria can help you analyze their suitability in different decision-making scenarios.

Ask a new question for Free

By Image

Drop file here or Click Here to upload

Math Problem Analysis

Mathematical Concepts

Voting Theory
Pairwise Comparison
Copeland's Method
Majority Condition

Formulas

Points in Copeland's Method: 1 point for win, 0.5 for tie, 0 for loss

Theorems

Majority Condition
Condorcet Criterion

Suitable Grade Level

College Level