Preferential block voting

Preferential block voting is a 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. 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

In preferential block voting, a preference voting 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.

Effects of preferential block voting

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 prefential 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

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