By-election - in Multi-member Constituencies

In Multi-member Constituencies

When one seat in a proportional representation constituency becomes vacant, the consequences vary. For example, a by-election may be held to fill just the vacancy or all the seats in the constituency be contested in the by-election.

Scotland and New Zealand still hold by-elections, despite having adopted the mixed-member proportional representation system, in which members are chosen by party lists. In both countries, by-elections where voters elect their preferred candidate are only used to fill a vacancy in a constituency seat. For example, the death of Donald Dewar resulted in a by-election for the constituency of Glasgow Anniesland. If a vacancy arises from the death or resignation of a party list member, the next unelected candidate on the party list is offered the seat. If that candidate has died or declines the seat, it is offered to subsequent candidates on the list until one accepts the seat. For example, on the resignation of Darren Hughes in March 2011, Louisa Wall was elected after all the five candidates above her on the New Zealand Labour Party's list declined the seat. The Republic of Ireland holds by-elections despite electing members in multi-member constituencies by the single transferable vote.

Alternatives to holding a by-election include:

1. choosing from those losing candidates at the previous election who choose to contest the recount to fill the vacancy, as in Tasmania or the Australian Capital Territory,
2. keeping the seat vacant until the next general election. This usually occurs if a vacancy arises shortly before a planned general election (within six months in New Zealand).
3. nominating another candidate with the same affiliation as the former member – typically, in list systems, the next candidate on the party list.

For the Australian Senate (where each State forms a multi-seat constituency voting by single transferable vote), the State Parliament appoints a replacement; in 1977 a referendum amended the Constitution to require that the person appointed must belong to the same political party (if any) as the Senator originally elected to that seat. Those Australian states with an Upper House elected by PR-STV (NSW, Victoria and South Australia) copy the federal Senate model, except for Western Australia, which holds a recount of ballots, with sitting members retaining their seats.