Almost two-thirds of the Facebook adverts around the Irish abortion referendum are so-called “dark ads” from unregistered campaigns, new data reveals.

The officially registered campaigns on Ireland’s 8th amendment have run hundreds of adverts on the social media site in the final weeks of the campaign, but these have been dwarfed by those from unregistered campaigners – justifying fears that dark ads could be influencing the vote.

The data comes from the Transparent Referendum Initiative (TRI), which has crowdsourced information on online adverts around Ireland’s referendum using the browser add-on, WhoTargetsMe.

The data builds a picture – though an incomplete one – of the flurry of adverts targeting Irish voters during the final weeks of highly-charged debate over abortion.

The data, which was analysed by Killian McLoughlin at the computational social sciences laboratory at University College Dublin, reveals that of the 1,281 partisan adverts the initiative has collected through the campaign:

• 749 (58%) were in favour of repealing the abortion ban

• 532 (43%) were in favour of keeping it

Earlier this month Facebook and Google announced they would no longer accept adverts on the referendum from overseas advertisers, such as US church groups – despite such ads being allowed under Irish election law.

However, it’s not clear whether that ban led to an end of adverts of that type on the Google and Facebook platforms, because so many of the adverts were untraceable.

McLoughlin said though it was impossible to separate out the impact on volume that the ban has had, “what we have seen is an end to identifiable overseas ads in our database since Facebook’s May 8th decision.

“Since then the number of Irish ads has grown exponentially, but the number of untraceable ads has also risen. While it is possible that these pages are Irish and we’re just unable to identify their precise source, they could also be international accounts.” 

The Transparency Referendum Initiative, says it has campaigned for an “open, truthful & respectful debate” ahead of today’s vote. It has not taken a public position on the referendum and it receives no external funding. 

Liz Carolan, one of the TRI’s volunteers, said that without the campaign’s efforts the effect of Facebook adverts on the campaign would have been impossible to measure.

“Without the volunteers who’ve helped us build the database of online ads, we would have no picture of what has happened in online spending,” she said. “As it stands, we still only have a partial picture – but that has led to ads being taken down, investigations being carried out and a response from the tech companies and politicians.

“Since Facebook’s overseas ad ban and Google’s political ad ban, we’ve seen a continued increase on the volume of ads – on Facebook new groups have continued to emerge placing ads, and online, other providers of ad space appear to have stepped in and filled the gap they left.”

The majority of the adverts tracked by the group do not clearly identify themselves as coming from campaigns registered with Ireland’s Standards In Public Office authority (SIPO), which oversees political conduct, disclosures of interest, and conduct.

The TRI data shows 38% of advertisers were registered with SIPO or were openly affiliated to a campaign which was, meaning that the overwhelming majority, 62% were not. Of those, McLoughlin’s analysis showed, 21% were from overseas campaigns or were entirely untraceable.

Some people have taken to online detective work to try to track down the source of some of the campaign’s untraceable campaigns.

Journalist-turned-entrepreneur Gavin Sheridan went viral on Twitter after spending a day trying to track down who was behind an online campaign ostensibly offering neutral information for those undecided on the vote, which in reality was a campaign from an organisation backing the abortion ban. 

The connection was only found thanks to the “undecided” site and the “protect the eighth” registered campaign sharing the same developer and reusing some code, allowing Sheridan and others to deduce the connection.

Sheridan explained that this was not illegal under Irish law, and nor was it unusual in the modern world of online campaign and dark advertising.

“What we saw with undecided8.org was relatively standard online ad tactics. Using Facebook and Google trackers to identify portions of the audience is not necessarily unusual. We just lack adequate laws on transparency and disclosure,” he said.

“When it comes to ads and darks ads there are a number of interconnected problems. A big problem is no-one knows what ads are running across any given platform.

“There are no regulations around deceptive ads and opacity around who is behind certain pages and websites. It is sometimes possible to trace, but not always, and there’s no legal obligations placed on platforms to tell us. There should be, particularly when some pages are cloaking their identity and purpose.”