Countback

In politics, the countback method is a way of filling casual vacancies. Casual vacancies are filled re-examining the ballot papers data from the previous election. The candidate who held the seat is eliminated, and a new election result is obtained by transferring votes that were originally allocated to the elected candidate at the time of their election to unsuccessful candidates. This process maintains the proportionality of the representation according to the voters' choice without the need and associated costs of holding fresh elections.

Uses
Countbacks are used in Malta, five Australian jurisdictions (the Australian Capital Territory, Tasmania, Victoria, and Western Australia, and at the local government level in New South Wales), and Cambridge, Massachusetts.

Problems
Countback methods are most often used together with the single transferable vote, which causes substantial problems. Countbacks vary by whether or not wasted and exhausted ballots are additionally used during the countback. The effect this has on the result of the countback depends on the differences in the next preferences of voters. Moreover, in STV systems that use exhausted ballots during countbacks, it becomes theoretically possible that the order of multiple resignations will affect who the ultimate replacements are - this is a consequence of the order of election as votes allocated to elected candidates are locked that value of which are no longer used in the determination of the election of further vacancies. Additionally, if ballots are allowed to be exhausted in the election, then by either method it remains possible that the chosen replacement will only meet a fraction of a quota of voters; when this fraction is particularly small, and therefore no similar candidates remain on the ballot, election rules may call for a different method of filling the vacancy to be used.

Insufficient candidates
Although the countback method is designed to select a replacement representing the same group of voters who elected the original candidate, it remains possible that no similar candidates remain on the ballot. In 1985 the Tasmanian parliament amended the electoral act to allow true by-elections if no candidates of the same party as the outgoing representative remained on the ballot; in this circumstance the party may request that a by-election be held, however this has not yet happened as most political parties and community groups now nominate a surplus number of candidates in order to fill any casual vacancies.