Public Choice

, Volume 101, Issue 3–4, pp 267–283 | Cite as

The Probability of Being Decisive

  • A.J. Fischer
Article

Abstract

The probability of a voter being decisive (PD), that is, of one vote affecting the outcome of an election, has generally been incorrectly calculated for the last twenty or more years. The method normally used is due to Banzhaf (1968) and generalised by Beck (1974). It assumes that voters know in advance how many people will vote for each candidate, which is clearly not the case. The correct formulation was given by Good and Mayer in 1975, but was ignored and has subsequently been all but forgotten since then. A simple explanation of these methods is given. Using the incorrect method, errors of magnitude of more than 10100 in calculating PD correctly can be made. The appropriateness of using a decision-theoretic formulation instead of a game-theoretic one is also discussed.

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Copyright information

© Kluwer Academic Publishers 1999

Authors and Affiliations

  • A.J. Fischer
    • 1
    • 2
    • 3
  1. 1.Health Care Evaluation UnitSt. George's Hospital Medical School, Cranmer Terrace, TootingLondonUnited Kingdom
  2. 2.University of AdelaideAustralia
  3. 3.Trinity CollegeCambridgeUnited Kingdom

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