Candidates are elected (winners) if their vote tally exceeds the electoral quota.
The system attempts to ensure factions are represented proportionally, without the need for official party lists, by having each winner elected with roughly the same number of votes.
The quota (sometimes called the threshold) is the number of votes that guarantees election of a candidate.
But in real-life elections, if it is allowed for valid ballots to not bear full rankings, it is common even under Droop for one or two candidates to be elected with partial quota at the end, as the field of candidates is thinned to the number of remaining open seats and as the valid votes still in play become scarcer.
The use of Droop leaves a full quota's worth of votes held by unsuccessful candidates, which are effectively ignored.
[3] Until all seats have been filled, votes are successively transferred to one or more "hopeful" candidates (those who are not yet elected or eliminated) from two sources: (In either case, some votes may be non-transferable as they bear no marked back-up preferences for any non-elected, non-eliminated candidate.)
In some systems, surplus votes are transferred only if they could possibly re-order the ranking of the two least-popular candidates.
Lower preferences piggybacked on the ballots may not be perfectly random and this may affect later transfers.
Such a method is used to elect the lower houses in the Australian Capital Territory and in Tasmania.
The Wright system is a reiterative linear counting process where on each candidate's exclusion the quota is reset and the votes recounted, distributing votes according to the voters' nominated order of preference, excluding candidates removed from the count as if they had not been nominated.
Increase the recipient's vote tally by the product of the ratio and the ballot's value as the previous transfer (1 for the initial count.)
Every preference continues to count until the choices on that ballot have been exhausted or the election is complete.
From May 2011 to June 2011, the Proportional Representation Society of Australia reviewed the Wright System noting: While we believe that the Wright System as advocated by Mr. Anthony van der Craats system is sound and has some technical advantages over the PRSA 1977 rules, nevertheless for the sort of elections that we (the PRSA) conduct, these advantages do not outweigh the considerable difficulties in terms of changing our (The PRSA) rules and associated software and explaining these changes to our clients.
Nevertheless, if new software is written that can be used to test the Wright system on our election counts, software that will read a comma separated value file (or OpenSTV blt files), then we are prepared to consider further testing of the Wright system.
[citation needed]This variation is used in Tasmanian and ACT lower house elections in Australia.
[9] The last bundle transfer method has been criticized as being inherently flawed in that only one segment of votes is used to transfer the value of surplus votes, denying the other voters who contributed to a candidate's success a say in the surplus distribution.
Two seats need to be filled among four candidates: Andrea, Brad, Carter, and Delilah.
This gives Brad 20 votes (exceeding the quota), electing him to the second seat: Other systems, such as the ones used in Ashtabula, Kalamazoo, Sacramento and Cleveland, prescribed that the votes to be transferred would be drawn at random but in equal numbers from each polling place.
An alternative means of expressing Gregory in calculating the Surplus Transfer Value applied to each vote is
[12] The effect of the Gregory system can be replicated without using fractional values by a party-list proportional allocation method, such as D'Hondt, Webster/Sainte-Laguë or Hare-Niemeyer.
The D'Hondt system is applied to determine how the surplus votes would be transferred - successive quotients are calculated for each hopeful candidate, one surplus vote is transferred to the hopeful candidate with the largest quotient, and the hopeful candidate's quotient is recalculated; this is repeated until all surplus votes have been transferred.
In the case of the Senatorial rules, since all votes are transferred at all stages, the recursion is infinite, with ever-decreasing fractions.
The Meek algorithm uses an iterative approximation to short-circuit the infinite recursion that results when there are secondary preferences for prior winners.
This process continues until all the Elected candidates' vote values closely match the quota (plus or minus 0.0001%).
[17] Warren is identical to Meek except in the numbers of votes retained by winners.
[18] The method used in determining the order of exclusion and distribution of a candidates' votes can affect the outcome, and multiple such systems are in use.
The general principle that applies to each method is to exclude the candidate that has the lowest tally.
Alternatives include excluding the candidate with the lowest score in the previous round and choosing by lot.
[clarification needed] The four types are: Quota breakpoints may not apply with optional preferential ballots or if more than one seat is open.
Quota breakpoint (based on the 2007 Queensland Senate election results just prior to the first exclusion): Running breakpoint (based on the 2007 Tasmanian Senate election results just prior to the first exclusion):