Black's method

Revision as of 14:04, 31 March 2020 by Psephomancy (talk | contribs) (add references)

Black's method chooses the Condorcet winner if it exists, but uses the Borda count instead if there is an ambiguity (the method is named for Duncan Black).[1]

Example:

 25 A>B>C
 40 B>C>A
 35 C>A>B

Borda scores are A 185, B 205, C 210. A pairwise beats B beats C beats A, so there is no Condorcet winner (because everyone has at least one defeat). So the Borda winner, C, wins.

Note that the winner of the Borda count is not necessarily in the Smith set.[2]

A Smith-efficient variant of Black's method could be used instead, to ensure someone in the Smith set will win.

References

  1. Black, Duncan (1987). The Theory of Committees and Elections. p. 66. ISBN 978-94-009-4225-7. Retrieved 2020-03-31.
  2. di Fenizio, Pietro Speroni (March 12, 2014). "Is there formal proof that Duncan Black's Electoral System is a Condorcet System?". ResearchGate. Retrieved 2020-03-31.