Same-sex marriage: What sway will 'undecided' voters have on the upcoming postal survey?

Same-sex marriage: What sway will 'undecided' voters have on the upcoming postal survey?

Same-sex marriage: What sway will 'undecided' voters have on the upcoming postal survey?

Updated 1 September 2017, 12:00 AEST

Is it possible we already have the data to tell us what the outcome of the upcoming postal survey on same-sex marriage will be?

Both the Yes and No campaigns to convince registered voters ahead of the upcoming postal survey on same-sex marriage are now well underway.

After the initial campaign by supporters of same-sex marriage to boost electoral enrolments among younger Australians, the focus of the Yes camp is now shifting to turnout.

Meanwhile, the No campaign strategists know they will get their best shot with older Australians and recent immigrants.

But is it possible we already have the data to tell us what the outcome of the survey will be?

Do surveys really show most Australians support same-sex marriage?

Undoubtedly yes, according to postdoctoral psychology researcher Dr Sharon Dane from the University of Queensland.

Dr Dane said over the past five years, polling and qualitative research had shown a steady increase in the number and proportion of Australians that think same-sex couples should be able to marry.

The drift towards greater support is true across both sides of the debate too: Australians who support same-sex marriage are becoming more strongly supportive, while those with weak levels of opposition are drifting into the undecided category.

"We know from scientific polling that's been done over the last five years at least that support, on average, is hovering around the 60 to 65 per cent," Dr Dane said.

"That doesn't mean there aren't extremes — some polls have found support at 58 per cent, and there's an extreme at the other end, which was 72 per cent."

She said the drift of "soft supporters" towards a stronger position on same-sex marriage was another clear trend.

"Strong supporters used to be in the low 30 per cent, they are now in the mid 40s," Dr Dane said.

"Strong No voters are now also shifting more over to a softer No."

Are polls a more reliable way to measure views than the upcoming postal survey?

The biggest nationally representative study of Australian households is the longitudinal HILDA survey, conducted by the Melbourne Institute.

HILDA has been asking its 17,000 respondents whether "homosexual couples should have the same rights as heterosexual couples do" since 2005, inviting them to rank their reaction on a scale of 1 to 7.

Of all the trends evident in the most recent 2015 HILDA dataset, the shift towards greater support for same-sex marriage is the clearest, according to professorial research fellow at the University of Melbourne, Roger Wilkins.

"We've seen a dramatic shift," he said.

"Between 2005 and 2015 we went from a clear majority disagreeing with that statement to a clear majority — I think it's around 60 per cent of people now agree, and most strongly agree."

Because the HILDA results are adjusted for the broader population, are drawn from surveys conducted in-person, and because participants are paid $35 each to participate, Professor Wilkins said the HILDA result was better than the postal survey answers will be.

"I have little doubt in my mind that when people are responding to this question they are thinking about rights to marriage, and it's pretty clear," he said.

So who hasn't made up their mind yet on same-sex marriage?

According to the HILDA numbers, most Australians already have a fairly strong view on same-sex marriage.

In fact, when asked to register their position on whether or not same-sex couples should have "the same rights as heterosexual couples do", only 12.4 per cent of HILDA respondents marked themselves as undecided.

Senior Research Fellow at the Institute for Social Science Research at the University of Queensland Francisco Perales has studied the 2015 HILDA numbers to work out who those people are.

And, according to his analysis, they are more likely than the rest of the population to be male, to live outside the major cities, and to be from immigrant backgrounds.

"They look very much like the people who tend to disagree with the statement that 'homosexual couples should have the same rights as heterosexual couples do'," Dr Perales said.

"But they are a fairly small group, only about 12 per cent, so I think there is an overwhelming majority of people who agree with the notion that homosexual couples should have the same rights as heterosexual couples."

Asked what his analysis means for the No and Yes campaigns, Dr Perales said the role of the undecided voter will be small.

"It's unlikely that this group is going to make a major difference, given their size," he said.

So, why isn't the same-sex marriage postal survey a done deal?

In a word: turnout.

All the researchers agreed the profile of a supporters of same-sex marriage and the profile of an opponent was pretty clear.

In general terms, the researchers said supporters were more highly educated, less religious, less likely to be from immigrant backgrounds, and more likely to live in inner cities or suburbs, with the inverse true for opponents.

Given that, Dr Dane said if a marriage plebiscite — as had originally been proposed by the Federal Government — were being held, the outcome would be fairly easy to call.

But because participation in the upcoming postal survey is voluntary, the result is harder to read.

"It's clear that there are more Yes voters than No — there are just more people who are pro," she said.

"But the issue is mobilising those Yes voters to vote, so the Yes campaign now is focusing on mobilisation, and it is not focusing on persuasion."

Conversely, Dr Dane said the key for a successful No campaign will be low turnout among young people and high turnout among immigrant groups.

And being able to get the comparatively small, undecided group to swing its way will also help.

"As has always been done in No campaigns, if you can get enough fear out there or confusion, people will revert back to safety," she said.

"People will say, 'let's just go with no to be on the safe side' — and that's what's been done with the Brexit vote and with other marriage equality campaigns in the US and Ireland."

The forms for the postal survey will start being sent out from September 12, and a final deadline for their return on November 7. The final results are due to be known on November 15.