And in the Senate, the Greens have won 14 Senate contests since they began, but even when Coalition preferences were directed to them, they never determined the result.* Greens candidate for Melbourne Adam Bandt is a strong chance to hold off Labor's Cath Bowtell, despite the Liberals pledging to preference the Greens last. Credit:Jason South Why don't Coalition preferences have a bigger impact? Three reasons. First, there are only two seats where they are likely to be distributed – Melbourne, and the inner Hobart seat of Denison, held by independent Andrew Wilkie. In 2010 the Greens came close to taking Grayndler from Deputy Prime Minister Anthony Albanese, or Sydney from Health Minister Tanya Plibersek. But the rising Liberal vote in NSW is almost certain to consign the Greens to finish third in both seats this time. Liberal preferences will not be distributed.

Second, inner city voters are independent types. A study by the Victorian Electoral Commission of voting in four inner city and four country seats at the 2006 election found that fewer than 50 per cent of voters followed their party's how to vote card. Inner city Liberals are even more individualistic. Most of them don't like head office telling them what to do; they make up their own minds. Moreover, one in five votes in Melbourne in 2010 was cast not at a polling booth, but in pre-poll, postal or absentee voting, where voters don't have how-to-vote cards to tell them what to do. In 2006, only 39 per cent of inner city Liberal voters followed the party ticket in allocating preferences – including just 30 per cent in the state seat of Melbourne. That is why the Greens narrowly lost the seat: 26 per cent of Liberals ignored the party ticket and gave their preferences to Labor. Even in 2010, when Bandt won the federal seat, 22 per cent of Liberal voters directed preferences to Labor. At the state election, Liberal head office switched sides and directed preferences to Labor. But 35 per cent of Liberal voters in the seats of Melbourne and Richmond ignored the direction, and gave their preferences to the Greens. You have to assume a similar distribution this time. If so, Labor would win the seat, based on 2010 voting, but with a majority of just 6000 votes, or 4.2 per cent. It's still a marginal seat, and it's quite possible that, with no other Lower House seats it can realistically win, the Greens could focus their resources on Melbourne and make up that margin.

The Greens are more worried about the impact of Liberal preferences favouring Labor in the Senate. Traditionally, the six Senate seats contested in each state split three-all between left and right, so that Labor and the Greens fight out the left's final seat. You would think that Liberal preferences would have a big impact in that contest. After all, 96 per cent of us vote for the party box in Senate contests, and only 4 per cent of us distribute our own Senate preferences. Yet history shows Coalition preferences have never won the Greens any seats in the past. They were almost called on in 2010, but Senator Lee Rhiannon won a quota for the Greens just before the Coalition preferences were to be counted.* In 2010, for example, the Greens won their Senate seats in Victoria and Tasmania on first preferences, and in Queensland, WA and SA at relatively early stages of the count, when the Coalition was still fighting for its final seat. To win three seats in any state, the Coalition will need to win 43 per cent of the vote. If it wins 45 per cent, for example – and in a crowded Senate contest, that will be difficult – it would be able to distribute just 2 per cent of votes as preferences.