On left, Democratic presidential candidate Hillary Clinton is speaking at New York University in New York on July 24, 2015. On right, US Republican presidential candidate Donald Trump exits the New York Supreme Court after morning jury duty on August 17, 2015 in New York. Both are scheduled to participate in presidential primary debates this week. (AFP PHOTO / KENA BETANCUR(Right)) / (DON EMMERT(Left)-/AFP/Getty Images)

As the Republican presidential hopefuls prepare for their last 2015 debate in Las Vegas tonight, and the Democratic candidates for Saturday in New Hampshire, many Americans are preparing to watch on two screens. They’ll watch the candidates, live, on television—and they’ll watch social media commentary on another device, right alongside.

That “dual screening” is becoming the norm. Does it change how we relate to politics?

Yes, it does. In our recently published study in the Journal of Communication we found that people who use social media to discuss broadcast election debates online are more likely to become engaged in politics as a result.

The technical stuff

Here are the technical details of how we studied this. We define dual screening as the complex bundle of practices that involve integrating, and switching across and between, live broadcast media and social media. To get inside how this works during big political media events, we spent several months devising and testing an innovative new research design.

We decided to combine some big data analysis with a large-response, event-specific panel survey. By that we mean that we wanted to identify a large sample of Twitter users who tweeted about the debates, survey them about their behavior immediately after the debates, and then survey them again just after election day, to see if how they experienced the debates influenced their levels of political engagement throughout the campaign.

Using this approach, we were able to study Twitter users who commented on Britain’s high-profile radio and television debates between Liberal Democrat party leader and deputy prime minister Nick Clegg and the leader of the right-wing anti-European Union UK Independence Party, Nigel Farage, during the elections to the European Parliament in 2014.

With some valuable help from New York University’s Social Media and Political Participation (SMaPP) lab, we identified social media users who tweeted about the Clegg-Farage debates. We collected about 453,000 tweets that had been posted by more than 103,000 unique users. We sent survey invitations to a random sample of 22,000 of these users. We received 1,634 responses within three days. Of these, 1,187 provided a Twitter handle or email address and agreed to be contacted again. This allowed us to survey these people again, immediately after election day.

“Talking” about politics on social media gets people more involved in politics in the real world

Here’s what we found. Those who commented on the debates live on social media and who followed the conversation through hashtags were more likely to get more involved in politics, even after we controlled for other likely influences. They became a little more likely to donate money, persuade someone to vote for a candidate, or go to a public meeting or protest.

Twitter users who more actively participated in the discussion about the debates on social media using hashtags like #NickvNigel, #CleggFarage and #europedebate came away more energized and engaged with politics.

In contrast, those who followed the debates more passively, such as simply watching or listening live, or only reading about the debates on social media, didn’t get more involved.

And respondents who accidentally encountered information about the debate because they had originally gone online to do something else also reported being more engaged in politics as a result.

Many people “watch” first on social media and only later on video

We found something surprising as well. Many people assume that people are watching the debates on TV first, and turning to social media on their other devices second. It wasn’t so.

Individuals used social media to gain valuable information about the debate even if they were not watching or listening live. Seventy-one percent of those surveyed said they read about the debates on social media as the debates happened, while only 53 percent actually watched or listened to the debates live. And about a third of individuals only chose to tune in to the debates after they had read about them on social media.

The limits of our study

There are pluses and minuses to the fact that we focused on Twitter users. We did it because that’s the most likely second screen for political debates. But that also means our findings should be interpreted carefully. The dual-screeners we surveyed are more likely to be male, highly educated, and interested in politics, so they are not representative of the general population or even of voters. But studying how this specific population behaves during these events is valuable because 22 percent of British citizens are on Twitter and 60 percent of UK Twitter users are using it while watching television.

We also benchmarked our sample against a survey we ran on British internet users in general, so we can say with some certainty that our respondents do represent UK internet users who post political content online.

Citizens’ discussions of political events on social media may be chaotic and at times unruly. But big broadcast media events now combine with social media discussion in ways that can be positive for democracy.

Republican presidential candidates face off Dec. 15 for the last time this year. Here's what you should look out for at the prime-time CNN debate. (Sarah Parnass/The Washington Post)

Cristian Vaccari is reader in politics, Andrew Chadwick is professor of political science and Ben O’Loughlin is professor of international relations in the New Political Communication Unit in the department of politics and international relations at Royal Holloway, University of London.