Polling showed close competition between support for the U.K. to “leave” or “remain” in the EU on the eve of the referendum. In early to mid-June, polls had indicated that voters favored leaving the EU, The Huffington Post polling model shows. But that dynamic reversed in the final days ahead of the referendum. Adding to a false sense that “remain” would prevail, additional surveys released on the day of the referendum showed a preference to stay in the EU edging out an inclination to exit.
One notable trend that emerged, however, was that online and telephone polling tended to yield different results. The results of online surveys ran neck-and-neck when respondents were asked if they supported leaving the EU in the months leading up to the referendum. Meanwhile, telephone surveys tended to favor the “remain” campaign, though there were exceptions. In an analysis of referendum polling, The Huffington Post reported: “the internet poll average estimated a 1.2-point lead for ‘leave,’ while live phone polls had ‘remain’ up by 2.6 percentage points,” concluding that “internet polls were clearly more indicative of the victory for ‘leave.’”
The U.S. presidential primary race also witnessed a split between online and live polling. Trump tended to perform better in online voter surveys relative to live interviews during the primary competition. As Andrew McGill wrote last December, one theory as to why that might be the case is that “a sizable percentage of poll respondents, though willing to punch a phone key to say they support Trump, are still too embarrassed to actually tell another human being.”
It’s not possible to say definitively that a similar dynamic was at work in Brexit polling, said John Curtice, a polling expert who tracks U.K. attitudes toward the EU and the EU referendum. “The trouble is that people can come up with theories as to why saying that a vote to leave would be socially unacceptable, while others might say that a vote to remain would be socially unacceptable,” Curtice said. “When you’re looking at a one-off event you don’t have the litmus test to pick up social desirability bias.”
Over the past few years, Olsen has been tracking how populist political parties fueled by working class voters have fared across Europe. He has observed that “working class populist parties, movements and candidates do better in polling the more anonymous it is,” and “quite often outperform the results predicted for them by pre-election polls.”
In Olsen’s view, “there seems to be a problem in pollsters worldwide inaccurately assessing the propensity of these voters to turn out and what they are going to do.” That might be because voters are less likely to accurately report their political convictions when talking to a person in a live interview out of fear they will be judged harshly, given that critics of conservative populism often criticize supporters of such political movements as xenophobic. It could also indicate that pollsters are underestimating the likelihood that working class voters will turnout to vote.