CPO-STV

It does this by incorporating some of the features of the Condorcet method, a voting system designed for single-winner elections, into STV.

CPO-STV aims to overcome the problems of tactical voting in traditional forms of STV, where a candidate can be eliminated at an early stage in the process that might have gone on to be elected later had they been allowed to remain in the contest.

If used for a single-winner election, CPO-STV becomes the same as Condorcet method, in the same way that traditional STV becomes instant-runoff voting (IRV).

In such cases, a more complicated procedure, known as a Condorcet completion method, must be used to determine the set of winners that are elected.

Traditional forms of STV differ in the manner in which they deal with the transfer of surplus votes.

Andrea and Carter have both reached the quota to begin with so, for the sake of simplicity, this example need show only the comparison of those outcomes which include both of these candidates as winners.

His votes all transfer to Delilah so that the tallies stand at: Carter has more than the quota and is present in both outcomes.

This matrix includes only the comparisons between Outcomes A, B, and C: The example above clearly illustrates the difference between CPO-STV and traditional forms of STV.

The differences between CPO-STV and traditional STV are analogous to those between Condorcet's method and instant-runoff voting.

The reason Delilah does not win under traditional STV arises from the particular stage at which she is eliminated from the count.

In traditional STV the order in which candidates are eliminated during the count is highly influential in determining the final result.

Advocates of CPO-STV argue that the sequence in which candidates happen to be eliminated in an election is in fact highly arbitrary and should not influence the result.

The actual effect of sequential exclusions is that the number of first or higher preferences a candidate receives is very important.

While CPO-STV does not eliminate the problem of monotonicity relating to STV it greatly reduces it, by creating fewer situations in which it would be possible for a voter to affect the outcome in this way.

Like all forms of proportional representation CPO-STV is likely to elect councils or assemblies in which no one party or faction has an absolute majority.

Like other forms of STV its use of preferential voting is likely to encourage candidates to appeal to a broad cross section of voters in order to garner lower preferences.

This characteristic might, however, be increased by the fact that lower preferences have a greater influence on the final result under CPO-STV than under traditional forms of STV.

Under both systems the ballot paper is the same and voting occurs by ranking the candidates in order of preference.

A hand count, therefore, is only likely to be feasible in simple elections with a small number of candidates and voters.