History of referendums shows turnout will be crucial

Turnout is key in any election. It can be pretty predictable, usually somewhere in the mid-60s judging by the last handful of elections since 1997: 66 per cent; 63 per cent ; 67 per cent; 69 per cent; 65 per cent.

Referendums, however, are different.

Turnout for the same-sex marriage referendum in 2015 was 61 per cent but for the children’s rights referendum in 2012 it was 34 per cent. The referendum to abolish the Seanad saw a 39 per cent turnout.

Turnout can be decisive. The first Nice Treaty referendum saw a 34 per cent turnout and was defeated; the second Nice treaty referendum saw a 50 per cent turnout and passed comfortably with a two-thirds majority.

Abortion referendum: Minister says formal result unlikely before 6pm

---

Islands go to the poll: turnout slow in abortion referendum

---

Maria Steen will take part in TV3 debate having previously pulled out

---

Miriam Lord: Don’t underestimate birds’ brains, says Danny Healy-Rae

---

What really matters, of course, is differential turnout – where different cohorts of the population turn out at different rates. For instance, older people are much more reliable voters in elections than younger voters. And where there is differential support for the proposition – ie where support is much stronger among, say, younger people – then turnout becomes even more important. And that is exactly the case in the present campaign.

Rural vs urban

"Rural Ireland tends to have a higher turnout in general elections," says Adrian Kavanagh, a political geographer in NUI Maynooth. "But referendums tend to be higher in urban areas, especially in the middle class areas of Dublin. These constituencies also tend to see higher Yes votes."

The single biggest division in the abortion referendum is on age grounds – younger people are much more likely to be Yes voters, and older people are more likely to be No voters. Indeed, if the referendum was run among those only over 50, it would be soundly defeated; if it was run among under 50s only, it would sail through.

There has rarely been such a stark division evident in polls.

Younger people, in the 18-30 age group, tend to be much poorer at turning out on election day. “Irish people used to have among the lowest turnouts anywhere for the 18-30 age group,” says Kavanagh. Turnout is improving among them, he says, but older people are much more likely to vote.

Yes campaigners stress the commitment of younger people to turn out on this occasion. There is considerable evidence on the streets of a strong campaign among younger people, with many citing the example of the same-sex marriage referendum in 2015 as an example of a strong youth turnout. However, this is entirely anecdotal. There was no exit poll on the day and no detailed post-election study, so there is no hard evidence for a big youth turnout in 2015.

The big unknown

Yes campaigners have also taken heart from a large number of people getting on the supplementary electoral register, although Kavanagh says this is always big, for a variety of reasons. Nonetheless, he confirms from his work studying the marked registers (ie the record of who voted), that voters who go to the trouble of putting themselves on the supplementary register are much more likely to vote on the day.

The results of recent referendums have tended to show a sharp decline for the Yes side compared to the final opinion poll. The gap in the marriage referendum was eight points , but others have been much bigger. This may be a difficulty not in gauging voter intention, but in judging who will turn up on the day.

Polls have suggested a strong lead for the Yes side. But turnout is the big unknown. “If it’s close,” says Kavanagh, “turnout will be crucial”.