Facebook says its ‘voter button’ is good for turnout. But should the tech giant be nudging us at all?

What do we really know about the influence of the 'voter button'?

On the morning of 28 October last year, the day of Iceland's parliamentary elections, Heiidis Lilja Magnisdottir, a lawyer living in a small town in the north of the country, opened Facebook on her laptop. At the top of her newsfeed, where friends' recent posts would usually appear, was a box highlighted in light blue. On the left of the box was a button, similar in style to the familiar thumb of the "like" button, but here it was a hand putting a ballot in a slot. "Today is Election Day!" was the accompanying exclamation, in English. And underneath: "Find out where to vote, and share that you voted." Under that was smaller print saying that 61 people had already voted. Heiidis took a screenshot and posted it on her own Facebook profile feed, asking: "I'm a little curious! Did everyone get this message in their newsfeed this morning?"

In Reykjavik, 120 miles south, Elfa ir Gylfadottir glanced at her phone and saw Heiidis's post. Elfa is director of the Icelandic Media Commission, and Heiidis's boss. The Media Commission regulates, for example, age ratings for movies and video games, and is a part of Iceland's Ministry of Education. Elfa wondered why she hadn't received the same voting message. She asked her husband to check his feed, and there was the button. Elfa was alarmed. Why wasn't it being shown to everyone? Might it have something to do with different users' political attitudes? Was everything right and proper with this election?