It is 35 years since Ireland introduced the eighth amendment to its constitution, effectively banning abortion in Ireland. Then, as now, the debate was fraught. Voters were courted with leaflets, posters, door-to-door campaigning and missives read out in churches.

But this is the first abortion referendum in which Facebook will play a role. Following the controversy around Cambridge Analytica and its influence on the US presidential election and Brexit referendum, there has been concern that outside influence could swing the vote, in a country with just 3.2m eligible voters.

In May Google announced a ban on all ads relating to the referendum and Facebook announced that it was blocking all foreign referendum advertising. However, Facebook is still a major factor in this campaign.

In an attempt to build a picture of how both sides of the referendum are using Facebook to influence voters, the Transparency Initiative Referendum has been examining adverts, including boosted posts, that have appeared in the feeds of 600 Irish-based Facebook users.

A Guardian analysis of almost 800 Facebook ads identified by the group has revealed major differences in how the two sides of the campaign have sought to influence voters ahead of Friday’s referendum.

The most obvious difference between the two sides of the campaign is the emotional language adopted by the no side compared with the more legalistic tone on the pro-choice yes side.

Dr Katharine Dommett, lecturer in the public understanding of politics at the University of Sheffield, said the yes campaign tended towards “more factual, procedural language”, pointing to a higher frequency of the use of the words “constitution”, “country”, “support” and “donate”. “These words are much more factual and action-oriented, whereas the other side is much more emotive,” she said.

For example, some of the most frequently used words on the no side included “baby” or “babies”, used 12 times as often as in the yes camp; “unborn”, used 22 times as often; and “life”, used nine times as often.



By contrast, the yes campaign’s most-used words focused on the legal aspects of the issue: it used “constitution” five times as much, “campaign” four times more often, and “amendment” twice as much.

While there were several words that were common to both campaigns, there were others which were almost exclusively used by one side and not the other.

One strongly relied upon – and criticised – campaign message on the anti-abortion side has been around Down’s syndrome. The term has been used in 15 adverts by the no side in the Transparency Referendum Initiative sample, whereas it does not surface in the yes sample.

By contrast, fatal foetal abnormality was not referenced at all in the no sample, but was the subject of six adverts for yes.



Dr Theresa Reidy, a political scientist at University College Cork, said the sample of Facebook ads “reinforced the messages that we have seen” in the broader campaign. “On the no side, the emphasis is very much on babies and mothers, whereas on the yes side it’s very much about healthcare and medical care in pregnancy and we see those words coming through, as well as words like ‘women’ and ‘choice’,” she said.

Striking too is the tendency for the no campaign to use more negative language: Reidy points to the use of “killing” or “killed” (used in 25 ads on the no side) as examples of negative campaigning.

“Some of the no ads are certainly more negative,” she said. While she acknowledged that it can be much harder for a no campaign to forward a positive message, there is some research indicating that negative campaigning may be effective.

“Research, mainly that carried out in the US, indicates that negative advertising is more memorable, people are more inclined to remember it, and they can identify it more with a particular candidate or side in an electoral contest.” However, there is also research suggests that it can also have a depressing effect on turnout: “Attack ads actually can discourage voters from participating.”

Both sides of the abortion referendum campaign use official data on the number of women who travel to the UK to avail of an abortion. However, the way they interpret these statistics can produce conflicting results.

Another theme of this campaign has been the way each side has undermined the claims of the other. This has been seen, not only in the two sides interpreting news stories differently, but also claims and counterclaims over posters being destroyed in the course of the campaign.



The two campaigns have also used Facebook for different purposes. Events made up almost a quarter of the adverts on the yes side, compared with less than 5% of those on the no side.

Methodology

The analysis is based on 788 Facebook ads (432 from the yes campaign, 356 from the no side) related to the Irish abortion referendum (as identified by the Transparency Initiative Referendum as of the evening of Sunday 14 May).

Two types of analysis were carried out. In the first instance, the text from all the ads was analysed to identify each individual word. A count was then carried out to establish how many adverts included each word. Comparisons between the yes and no sides were weighted to reflect the differing number of adverts carried by each.

Additional reporting by Sinead Baker and Victòria Oliveres

