Single transferable vote: Difference between revisions

Many writers consider the [https://en.wikipedia.org/wiki/Single_transferable_vote single transferable vote] to be a semi-proportional system because of its substantial favoritism towards major parties, generally caused by a combination of the [https://en.wikipedia.org/wiki/Droop_quota Droop quota] in small districts, as well as the substantial degree of [https://en.wikipedia.org/wiki/Vote_management vote management] involved when there are [https://en.wikipedia.org/wiki/Exhausted_ballot exhausted ballots].<ref name="NorrisChoosingElecSys2">{{cite web|url=http://www.hks.harvard.edu/fs/pnorris/Acrobat/Choosing%20Electoral%20Systems.pdf|title=Choosing Electoral Systems: Proportional, Majoritarian and Mixed Systems|last=Norris|first=Pippa|year=1997|publisher=[[Harvard University]]}}</ref> On the other hand, some authors describe it as a proportional system, on the grounds that it is theoretically [https://en.wikipedia.org/wiki/Proportionality_for_solid_coalitions weakly proportional] in the limit of infinitely-large constituencies.<ref>David M. Farrell Electoral Systems (2011)</ref> However, it is worth noting that STV is only proportional for [https://en.wikipedia.org/wiki/Solid_coalition solid coalitions], i.e. if voters rank candidates first by party and only then by candidate. As such, the proportionality of STV breaks down if voters are [https://en.wikipedia.org/wiki/Cross-cutting_cleavage split across party lines] or choose to support candidates of different parties.

A major complication with proportionality under STV is the need for [https://en.wikipedia.org/wiki/Electoral_district constituencies]; small constituencies are strongly disproportional, but large constituencies make it difficult or impossible for voters to rank large numbers of candidates, turning the election into a ''de facto'' [https://en.wikipedia.org/wiki/Electoral_list party list] system, where voters lack any meaningful information about the candidates on their ballot.

The degree of proportionality nationwide is strongly related to the number of seats to be filled in each constituency. In a three-seat constituency using the [https://en.wikipedia.org/wiki/Droop_quota Droop quota], a full quarter of the vote is [https://en.wikipedia.org/wiki/Wasted_vote wasted]. In a nine-seat constituency, only a tenth of the vote is [https://en.wikipedia.org/wiki/Wasted_vote wasted], and a party needs only 10% of the vote to win a seat. Consequently, the best proportionality is achieved when there are a large number of representatives per constituency. The [https://en.wikipedia.org/wiki/Hare_quota Hare quota] is theoretically [https://en.wikipedia.org/wiki/Seat_bias unbiased], allowing some of its errors to cancel out across the country. However, it also increases the vulnerability of STV to [https://en.wikipedia.org/wiki/Vote_management vote management] by large parties, allowing them to win the same number of seats they would have won under Droop.

In the [https://en.wikipedia.org/wiki/2011_Irish_general_election 2011 Irish general election], Fine Gael received 45.2% of the seats with just 36.1% of the first preference votes.In the [https://en.wikipedia.org/wiki/2020_Irish_general_election 2020 Irish general election], the [https://en.wikipedia.org/wiki/Labour_Party_(Ireland) Labour Party] received 50% more votes than the [https://en.wikipedia.org/wiki/Social_Democrats_(Ireland) Social Democrats], but both parties won the same number of seats. [https://en.wikipedia.org/wiki/Ireland_(country) Ireland] uses districts of 3-7 members.

Similarly, the [https://en.wikipedia.org/wiki/1998_Northern_Ireland_Assembly_election 1998 Northern Ireland elections] resulted in the [https://en.wikipedia.org/wiki/Ulster_Unionist Ulster Unionists] winning more seats than the [https://en.wikipedia.org/wiki/Social_Democratic_and_Labour_Party Social Democratic and Labour Party] with a smaller share of the vote.

The proportionality of STV can be controversial, especially in close elections like the 1981 election in Malta. In this election, the [https://en.wikipedia.org/wiki/Labour_Party_(Malta) Maltese Labour party] won a majority of seats despite the Nationalist Party winning a majority of first preference votes. This caused a constitutional crisis, leading to a provision to provide bonus seats in case of disproportional results. These bonus seats were needed in 1987, 1996, and 2008 to prevent further [https://en.wikipedia.org/wiki/Electoral_inversion electoral inversions].