Correlated Instant Borda Runoff

Correlated Instant Borda Runoff (CIBR) is a preferential voting system for single-winner elections, devised by Ken Kuhlman in May 2005 in order to reduce Borda's susceptability to clones.

Procedure

Candidates are scored according to the Borda count. The Borda loser of the most-correlated pair of candidates is eliminated. The process is repeated until only one candidate remains.

Example

Imagine that Tennessee is having an election 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 lives in these four cities, and that everyone wants to live as near the capital 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, near the center of Tennessee
• 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)
1. Memphis
2. Nashville
3. Chattanooga
4. Knoxville
1. Nashville
2. Chattanooga
3. Knoxville
4. Memphis
1. Chattanooga
2. Knoxville
3. Nashville
4. Memphis
1. Knoxville
2. Chattanooga
3. Nashville
4. Memphis

The Borda scores for the four candidates are:

• Nashville: 194
• Chattanooga: 173
• Memphis: 126
• Knoxville: 107

If "correlation" is defined as third-order correlation, then the most-correlated pair is Chattanooga and Knoxville. Knoxville has fewer Borda points and so is eliminated. After this elimination, the Borda scores for the remaining candidates are:

• Nashville: 126
• Chattanooga: 90
• Memphis: 84

and the correlations are:

• Nashville & Chattanooga: 100%
• Nashville & Memphis: 74%
• Chattanoogs & Memphis: 26%

The new most-correlated pair is Nashville and Chattanooga. Chattanooga is the Borda loser of this pair and is eliminated. The Borda scores of the remaining pair of candidates are:

• Nashville: 58
• Memphis: 42

Memphis is eliminated, and Nashville wins.

CIBR passes:

It fails: