Participation criterion

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The participation criterion is a voting system criterion for evaluating voting systems. It has been defined as follows:

Douglas Woodall's definition: The addition of a further ballot should not, for any positive whole number k, reduce the probability that at least one candidate is elected out of the first k candidates listed on that ballot.
Mike Ossipoff's definition: Adding one or more ballots that vote X over Y should never change the winner from X to Y.

Plurality voting, Approval voting, cardinal ratings, and Borda count all satisfy the participation criterion. All Condorcet methods, Bucklin voting, Majority Choice Approval, and IRV fail.

If a voting system fails the participation criterion, then a particularly unusual strategy of not voting can, in at least some circumstances, help a voter's preferred choice win.

The participation criterion for voting systems is one example of a rational participation constraint for social choice mechanisms in general.

1 Quorum requirements
2 See also
3 References
4 External links

[edit] Quorum requirements

The most common failure of the participation criterion is not in the use of particular voting systems, but in simple yes or no measures that place quorum requirements. A public referendum, for example, that required majority approval and a certain number of voters to participate in order to pass would fail the participation criterion, as a minority of voters preferring the "no" option could cause the measure to fail by simply not voting rather than voting no. A referendum that required a minimum number of yes votes (not counting no's), by contrast, would pass the participation criterion.