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Borda Count


The Borda count is a voting rule in social choice theory that assigns evenly spaced scores to the positions in each voter's complete ranking of the candidates without ties. With m candidates, each voter awards m-1 points to the first-ranked candidate, m-2 to the second, and so on down to 0 for the last (Saari 1999, p. 10568).

If r_i(c) is the position of candidate c in voter i's ranking, with position 1 best, then the total score over n voters is

 S(c)=sum_(i=1)^n[m-r_i(c)].

The candidates attaining the maximum score are the winners. Ties require a separate tie-breaking rule if a single winner is wanted. Using the scores m, m-1, ..., 1 gives the same ranking of candidates, since it adds n to every total.

Each voter contributes one point to a candidate for each other candidate ranked below it. Thus S(c) also counts the individual pairwise preferences for c over its opponents. This is different from counting victories in pairwise majority comparisons.

For example, suppose three voters rank A above B above C, while two rank B above C above A. The total scores for A, B, and C are 6, 7, and 2. Here A is the Condorcet winner and is ranked first by a majority, yet B wins the Borda count.


See also

Condorcet Winner, Social Choice Theory

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References

Numberphile. "Telescope Time Without Tears." May 7, 2015. https://www.youtube.com/watch?v=7c0CoXFApnM.Saari, D. G. "Chaos, but in Voting and Apportionments?" Proc. Nat. Acad. Sci. USA 96, 10568-10571, 1999. https://doi.org/10.1073/pnas.96.19.10568.

Cite this as:

Weisstein, Eric W. "Borda Count." From MathWorld--A Wolfram Resource. https://mathworld.wolfram.com/BordaCount.html

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