Voting system criterion

From Wikipedia, the free encyclopedia

It has been suggested that this article or section be merged with Voting system#Criteria in evaluating voting systems. (Discuss)

A voting system criterion is a formally defined pass/fail criterion by which a voting system may be assessed. They are usually defined such that they only depend on the inputted votes and the resulting output of the voting system, but they may also refer to the necessary time and space complexities associated with determining the result.

A simple example is the majority criterion, which says that if a candidate is the first choice of a majority of voters, it should win. Plurality satisfies this criterion, while Borda fails it.

Passing one criteria can automatically imply passing other criteria, but can also imply failing others. For example, the Condorcet criterion implies the majority criterion, but also simultaneously implies the failure of the consistency criterion (i.e. is incompatible with it). In fact, noted mathematical results like Arrow's theorem and the Gibbard-Satterthwaite theorem are in essence statements of the impossibility of satisfying certain combinations of criteria.

In light of this, assessing the worthiness of any voting system depends on which criteria an observer considers important enough to be satisfied by the system.

[edit] List of voting system criteria

Criteria besides those listed at Category:Voting system criteria include:

The New Zealand Royal Commission on the Electoral System defined ten subjective criteria for the evaluation of voting systems.

Bayesian regret is an objective numerical measure of quality of a voting system that is sensitive to subjective assumptions about the candidates and electorate. Its least contentious use is to give best-case and worst-case values for a given system.