VBV

From Electowiki
Jump to: navigation, search

VBV (for "Venzke Bucklin Variant") is a three-slot method defined by Kevin Venzke as an attempt to improve the Later-no-harm performance of MCA. See also IBIFA by Chris Benham, which could be seen as a similar attempt that doesn't sacrifice FBC or monotonicity.

Definition

  1. The voter submits a three-slot ratings ballot (preferred, approved, and the default: disapproved).
  2. Identify the candidate with the most top ratings (the "TRW").
  3. Find the "tentative winner": the candidate who is preferred or approved on the greatest number of ballots, except don't count any "approved" votes from ballots that rate the TRW as preferred.
  4. If the TRW and the tentative winner are the same candidate, elect that candidate.
  5. Otherwise, elect the candidate who is preferred or approved on the greatest number of ballots. (The ballots preferring the TRW are not treated differently this time.)

Comments

The idea behind this method is that voters preferring the most-preferred candidate (the TRW) receive a privilege: They do not have their lower preference(s) counted unless the TRW is not going to win. This is a Later-no-harm-like guarantee that works similarly to IRV. All the other voters have their preferred and approved ratings counted equivalently, however.

The method sacrifices FBC and monotonicity basically because only one candidate's supporters can receive the privilege. It's possible that a candidate can win when a certain other candidate is the TRW, but not when they are the TRW themselves.

Example

Tennessee's four cities are spread throughout the state

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 on Wikipedia, the state's largest city, with 42% of the voters, but located far from the other cities
  • Nashville on Wikipedia, with 26% of the voters, near the center of Tennessee
  • Knoxville on Wikipedia, with 17% of the voters
  • Chattanooga on Wikipedia, 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

Suppose that the voters place their first preference in the top slot and their second preference in the middle slot, leaving the bottom two preferences unvoted.

Memphis is the top-ratings winner, so we count all the preferences aside from the middle-slot Nashville preferences cast by the Memphis supporters. The result is that Chattanooga is the "tentative" winner, since all 58 non-Memphis voters voted for Chattanooga. Since Memphis is not winning, their middle slot preferences are counted. This brings Nashville's vote count up to 68 in comparison to Chattanooga's 58, so Nashville wins.