How the new Senate voting system works

Dugald Monro

Professional Associate with the Institute of Governance and Policy Analysis, University of Canberra.

With the election behind us, and the Senate votes still rolling in, there is still some confusion as to how the new system works. Indeed, there has been much speculation as to how it will affect the results, especially whether minor parties will be wiped out. Little attention has been paid to whether the new system will fully reflect the views of voters and how voters should vote to reflect their views. Malcolm Turnbull praised the new system saying  “….it gives the power, the choice, back into the hands of voters”. But if many voters filled in only one or a few preferences, the result may not reflect their views.


The Senate system is not a simple proportional representational system; it is a preferential–proportional system. In a simple proportional system seats are allocated in accordance to the number of first preference votes a party receives. In a preferential-proportional system such as the Senate, first preference votes determine whether a candidate has a quota, but where first preferences do not give quotas to enough candidates to fill all the seats, lower preferences are counted. If we apply the Senate quota formula to a single member electorate, such as a House of Representatives seat, the quota is 50%+1 vote. In the House of Representatives if a candidate receives a majority (50%+1) they are elected. If  no candidate obtains a majority the least popular candidate is excluded and their preferences distributed. This continues unto one candidate receives a majority after preferences. The Senate system applies a similar logic to multi-member electorates with achieving a quota before or after preferences being the goal instead of achieving a majority.


Under the new Senate voting system voters were instructed to fill in six preferences if voting above the line, and twelve if voting below the line. More may have been filled in if the voter wishes. Under a “savings” provision a vote will be regarded as valid even if only one preference is filled in above the line, or six below. 


Under the old system a voter voting above the line filled in only one preference but was effectively voting to the last preference. The order of preferences after the first preference was chosen by the voting ticket lodged by the party, not by  the voters themselves.


With optional preferences, filling in less than all possible preferences can reduce the influence of the vote. The way the Senate vote is counted quite low preferences, well beyond six or twelve, can affect the result. Surpluses from those candidates who achieve a quota are distributed. In practice all the candidates’ votes are distributed at a fractional value so that the total equals the number of surplus votes. The fraction distributed varies from very small to reasonably significant.  After surpluses have been distributed, if there are still seats to be filled the lowest candidate is eliminated and their preferences distributed. This process continues until all seats are filled. Where all preferences have been filled in, a vote (or a fraction of it) remains alive until the last Senate seat in the State or Territory has been filled. Should a voter give the last two candidates still in the count their last and second last preferences they would influence the result between those two candidates. 


Under the new system voters do not fill in all preferences, whether voting above or below the line, their votes drop out (exhaust) once the last shown preference has been counted. Thus they have no influence on any seats still remaining.


Surpluses from major parties, as well as preferences from eliminated candidates, can prove decisive in deciding the final seats. In 2013, in both Victoria and Tasmania ALP surpluses helped elect Green candidates, who were the second last candidates’ elected. In each case surpluses from the Greens, which included a fraction of ALP surpluses, ended up helping a minor party candidate (Motoring Enthusiasts and Palmer United) defeat the Liberal candidate for the last seat.


It is very hard to predict which candidates will be fighting for the last seat.  Looking at the last two Senate elections (2013 and 2010) we see that in many cases the last seat has been between a major party (which one varies) and a minor party. However there have been instances of the last seat being between both major parties or just between minor parties. If you voted for a major party that did not end up in the contest for the last seat, would you prefer to see any minor party succeed rather that the other major party? If so you would need have needed to fill in all preferences to cover this. Was there a candidate you really did not want see elected, and would prefer any other candidate to them? Again filling in all preferences would have been the only way to ensure that your vote expressed your view. Certainly something to keep in mind for the future.

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