The Tasmanian electorate of Denison at the 2010 Federal Election is an interesting case study of preferential voting in action.
The seat had been held by the ALP since 1987, although the sitting member, Duncan Kerr, retired at the election. The Labor, Liberal and Greens candidates were joined by a candidate from the Socialist Alliance and an independent, Andrew Wilkie.
The image below shows that Wilkie came third on primary votes, behind the Labor and Liberal candidates. The Greens were in fourth place and the Socialist Alliance in fifth. No candidate had an absolute majority of 50% + 1. This meant that preferences had to be distributed until someone secured 50% + 1.
Because she had the lowest number of votes, the Socialist Alliance candidate was excluded first. The allocation of her preferences did not change the order: the ALP still led, the Liberals were second and Wilkie remained in third place.
The Greens candidate now had the lowest number of votes and he was excluded. His preferences pushed Wilkie into second place, behind Labor, with the Liberals in third place. Still no-one had 50% + 1.
The third and final exclusion was the Liberal candidate. His preferences went to Wilkie by a margin of 79% to 21%. This ensured that Wilkie reached 51.21%, an absolute majority, against the Labor candidate on 48.79%.
Thus, from a third place primary finish, Wilkie was able to win the seat on preferences from three of the other four candidates.
Wilkie’s 51.21% consisted of 21.26% of voters who had cast their number 1, or primary, vote for him, and preferences from another 29.95% of voters who had given their primary vote to the Socialist Alliance, Greens or Liberal candidates. In the end, Liberal Party preferences were decisive in pushing Wilkie into the lead.
Preference flows in Denison at the 2010 Federal Election.
Source: Australian Electoral Commission 2013 Pocketbook, p56. The page is reproduced here under the terms of its Creative Commons licence.