Sri Lankan contingent vote
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In Sri Lanka a variant of the contingent vote electoral system is used to elect the President. As under the conventional contingent vote, in an election held using the Sri Lankan form of the contingent vote each voter ranks the candidates in order of preference, and if no candidate receives an overall majority of first preference votes on the first count then all but the two leading candidates are eliminated and their votes redistributed to help determine a winner in a second and final round. However, whereas under the ordinary form of the contingent vote voters can rank all of the candidates in order of preference, under Sri Lankan CV the voter only expresses her top three preferences. Sri Lankan CV has been used for presidential elections there since 1982.
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[edit] Voting and counting
Each voter ranks three candidates in her order of preference. In other words she gives a '1' to her first preference, a '2' to her second choice and a '3' to her third preference. In the first round of counting only first preferences are tallied. If any candidate has an overall majority of votes (i.e. more than half) at this stage then are declared elected. If no candidate has a majority then all candidates except the two with most first preferences are eliminated and the count proceeds to a second round. In the second round any voter whose first preference has been eliminated has his vote transferred to whichever of the two remaining candidates he has ranked next (but only if he has ranked at least one of the two). The candidate with the most votes is then declared elected.
[edit] Counting the votes
In the first round, if a candidate has the support of an absolute majority (i.e. more than half) of the total number of first preferences expressed they are deemed elected. If no candidate has such a majority then all candidates except the two who have received the largest number of first preferences are eliminated and the count proceeds to a second round.
In the second round any voter whose first preference has been eliminated has their vote transferred to the candidate of their second preference, but only if their second choice has not also been eliminated. If their second choice has also been eliminated then their vote is transferred to their third choice (provided that the third candidate has also not been eliminated). The candidate with the most votes is then declared elected.
[edit] An example
Imagine that the population of Tennessee, a state in the United States, is voting on the location of its capital. The population of Tennessee is concentrated around its four major cities, which are spread throughout the state. For this example, suppose that the entire electorate live in one of these four cities, and that they would like the capital to be established as close to their city as possible.
The candidates for the capital are:
- Memphis, the state's largest city, with 42% of the voters, but located far from the other cities
- Nashville, with 26% of the voters
- Knoxville, with 17% of the voters
- Chattanooga, with 15% of the voters
The preferences of the voters would be divided like this:
| 42% of voters (close to Memphis) |
26% of voters (close to Nashville) |
15% of voters (close to Chattanooga) |
17% of voters (close to Knoxville) |
|---|---|---|---|
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The count would proceed as follows:
| Memphis | Nashville | Chattanooga | Knoxville | |
|---|---|---|---|---|
| Round 1 | 42 | 26 | 15 | 17 |
| Round 2 | 42 | 26 | 32 | |
| Round 3 | 42 | 0 | 58 |
- Round 1: First preferences are tallied and no candidate has a majority.
- Round 2: Chattanooga has fewest votes so is excluded. Its votes all transfer to Knoxville but there is still no candidate with a majority.
- Round 3: Nashville is excluded. Nashville's supporters have Chattanooga as their second preference but Chattanooga has already been excluded, so instead the votes are transferred to their third choice, Knoxville. Knoxville now has a majority of votes so is declared elected.
- Winner: Knoxville
[edit] Potential for tactical voting
Sri Lankan CV is open to the same forms of tactical voting as other forms of the contingent vote. These include the tactics of 'compromise' and 'push over'. However the fact that voters are only permitted to express three preferences makes it especially vulnerable to 'compromise'. This is because it makes it necessary for voters to express either a first, second or third preference for one of the two leadings candidates if they wish to influence the result of the election. If lower preferences were allowed then the voter would, in many circumstances, be able to give her first three preferences to her three favourite candidates, even if neither was likely to be elected; if all three had only minor support then the voter could still influence the election by using her fourth or subsequent preferences to support more popular candidates.
