A turnout near 80% means the Yes vote for marriage equality is a practical certainty to win

A same-sex marriage rally in Sydney. Photo: Saeed Khan/ AFP/ Getty Images.

The Australian Bureau of Statistics has released what will be close to the final participation rate in the postal survey on marriage equality, and it is a staggeringly high 78.5%.

The ABS says an estimated 12.6 million Australians have returned their votes.

The turnout of 78.5% is extraordinary, given the survey was voluntary and required people to physically mail their ballot papers.

For comparison, the turnout in the UK’s Brexit referendum was 72%. Turnout in last year’s US presidential election was 60%. Ireland’s national referendum on marriage equality had a 60.5% turnout.

The sheer mass of votes cast in Australia now makes it a practical certainty that the Yes campaign will win. John Howard famously said that politics was “remorselessly governed by the laws of arithmetic”, and the maths at this level of turnout simply do not stack up in the No campaign’s favour.

With around 16.05 million people eligible to participate, the No vote would have to secure over 6.3 million of the 12.6 million votes cast to win. That is 40% of the total number of eligible voters.

Opinion polls this year have consistently shown around one-third of voters are opposed to same-sex marriage, with a further 10% undecided. (For example, a Newspoll published in August found 63% support for Yes, 30% for No, and 7% undecided.)

It just so happens that 6.3 million votes — roughly the level of a majority in a 12.6 million vote poll — is just under 40% of the total 16 million-plus eligible voters.

So, assuming the polls are broadly correct, the No camp needs to:

  • secure a 100% turnout among its supporters (impossible);
  • count on a very low turnout from the Yes side; and
  • secure practically all of the undecideds.

Even assuming a very high turnout for the No camp, every percentage point below 100% in turnout means it has to gain another 63,000 votes from undecideds or Yes voters just to stay in touch with keeping 50% of the total amount of votes cast.

But let’s assume turnout is roughly evenly split across the Yes and No campaigns. No simply can’t win, unless the polls are wildly, hopelessly wrong in consistently finding strong majority support in the community for same-sex marriage.

As ANU demographer Liz Allen pointed out this afternoon, a roughly two-thirds vote in favour would be a majority not just of survey ballots but of all eligible voters in Australia.

So it’s time to call it. The likelihood of a No campaign is now mathematical only. It isn’t a practical possibility. We’ve seen political shocks around the world but — barring the No campaign defying all the normal arithmetic of politics — this will not be one of them.

So when the results are announced next Wednesday, there will be a strong majority for Yes, and it’ll be a great day for the gay community and for the country.

The only thing left to do will be to see if Prime Minister Malcolm Turnbull can stick to his word and legalise gay marriage by Christmas.

Given his government is engulfed by a citizenship crisis, that might not be as straightforward as when he gave the commitment a couple of months ago.

*This article has been updated to correct the calculation on how many votes the No campaign needs to win to offset each percentage point loss of turnout from its supporters.

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