Preferential block voting

From Wikipedia, the free encyclopedia
Jump to: navigation, search

Preferential block voting is a majoritarian voting system for electing several representatives from a single multimember constituency. Unlike the single transferable vote, preferential block voting is not a method for obtaining proportional representation, and instead produces similar results to plurality block voting, of which it can be seen as the instant-runoff version. Under both systems, a single group of like-minded voters can win every seat, making both forms of block voting nonproportional.

Casting and counting the ballots[edit]

In preferential block voting, a ranked ballot is used, ranking candidates from most to least preferred. Alternate ballot forms may have two groupings of marks, first giving n votes for an n seat election (as in traditional bloc voting), but also allowing the alternate candidates to be ranked in order of preference and used if one or more first choices are eliminated.

Candidates with the smallest tally of first preference votes are eliminated (and their votes transferred as in instant runoff voting) until a candidate has more than half the vote. The count is repeated with the elected candidates removed and all votes returning to full value until the required number of candidates is elected. This is the method described in Robert's Rules of Order for electing multiple candidates to the same type of office.[citation needed]

Effects of preferential block voting[edit]

With or without a preferential element, block voting systems have a number of features which can make them unrepresentative of the diversity of voters' intentions. Block voting regularly produces complete landslide majorities for the group of candidates with the highest level of support. Under preferential block voting, a slate of clones of the first winning candidate are guaranteed to win every available seat. Although less representative, this does tend to lead to greater agreement among those elected.

Usage of preferential block voting[edit]

Block voting was used in the Australian Senate from 1901 to 1948; from 1918, this was preferential block voting.

Ballots[edit]

Rank ballot Hybrid ballots
Preferential bloc voting ballot 3.png Preferential bloc voting ballot 1.png Preferential bloc voting ballot 2.png
Three example ballots for a two-seat election, the first using a pure ranked ballot, and the second using a plurality block voting ballot for the initial vote, and ranking only the alternate preferences. The hybrid ballots are intended to clarify the fact that the top n choices are counted simultaneously, and the ranked choices are used conditionally based on elimination.