The run-up to Election Day might be exposing key flaws in public polling.
In the final days of the presidential race, the public polling has settled into a mostly consistent equilibrium: Hillary Clinton leads Donald Trump both nationally and in most key states, but by a narrower margin than last month, and not by enough to be assured of victory next week.
It’s been a bumpy road to that consensus, however, one marked by wildly careening results in recent days. Campaign professionals say the run-up to the election is exposing key flaws in the public polling conducted by news organizations and academic institutions.
The most obvious flaw is that the polls are overstating sudden fluctuations to the American people, say campaign pollsters whose own data is far more stable — even amid news events that rival the most creative political fiction.
“One of the reasons that I know the polling doesn’t move this much,” said Democratic pollster Nick Gourevitch, “is because any time we do a project internally using many, many interviews — the polling doesn’t move this much.”
It’s not a new phenomenon: After the 2012 election, President Barack Obama’s campaign bragged about its internal polling, which was far more stable relative to public polling.
While the public polls are almost uniformly more volatile than private data, the ABC News/Washington Post tracking poll — which over the past two weeks resembles a seismograph during a magnitude-8 earthquake — is taking it to another level.
The poll, which has been releasing new results daily, has swung wildly from its launch immediately after the final Clinton-Trump debate to the present time.
In the first iteration of the ABC/Post poll, conducted Oct. 20-23, Clinton led by a commanding 12-point margin, 50 percent to 38 percent. But in the following four-day rolling sample, conducted Oct. 24-27, the race had changed drastically: Clinton led Trump only by 2 points, 47 percent to 45 percent. That’s where the race stood Thursday — Clinton at 49 percent and Trump at 47 percent. At one point earlier in the week, Trump had a 1-point advantage for a day.
Other polls also differed dramatically in October, particularly those in contested states, with some pollsters showing results that swung from survey to survey. A University of New Hampshire survey in mid-October gave Clinton a 15-point lead, but that was down to 7 points in a UNH poll two weeks later.
Now, two polls out Thursday show a neck-and-neck race in the smallest battleground on the swing-state map.
It’s a similar story in Virginia — another battleground state where Clinton has led for most of the campaign, but where new polls this week vary greatly between a solid Clinton lead and a slight Trump edge.
“The state-by-state public polls are just sort of all over the place,” said Robert Blizzard, a pollster at the Republican firm Public Opinion Strategies.
Campaign pollsters point to a handful of factors to explain the volatility of public polling, compared with their own private data.