Everywhere I went Monday, conservatives were spooked by a Gallup poll showing President Obama with a six-point lead over Mitt Romney. Then on Tuesday, a Washington Post/ABC News poll had the margin down to a single-point Obama edge. What is going on?
As Election Day draws closer, most major public-opinion surveys shift from interviewing registered voters to interviewing those whom they identify as “likely voters.” The transition from polling “registered voters” to predicting who will actually vote is a tricky one and can involve some turbulence and differences between pollsters. Furthermore, some organizations make the switch earlier than others — in the case of this week’s polls, Gallup’s was of registered voters, the WP/ABC one was of likely voters. And that could have made the difference.
As Nate Silver, the statistics guru of the New York Times, reports, “In the past six presidential election years, the shift to likely voter models has always helped the Republican candidate, but the difference has also always been small.” Pollster Scott Rasmussen argued during the 2010 elections that his polls, which always interview only those voters he determines are most likely to vote, are more accurate. This group, he says, is trending more conservative these days because opponents of Obama’s policies are highly motivated to vote. Pollster John Zogby says polls tend to oversample Democrats, especially blue-collar women, who often don’t vote. Thus, “the results may be skewed toward the Democrats.”
Complicating the search for likely voters is the fact that people like to tell pollsters they plan to fulfill their civic duty and vote. A typical September poll will find three-quarters of registered voters saying they plan to vote in November. In reality, about a third of those won’t show up. Pollsters try to determine who will make up the actual electorate by asking people if they know when Election Day is, if they watched any of the debates, or if they have filled out their sample ballot.
Another factor this year may be an “enthusiasm gap” working against Barack Obama. Such a gap is hard to measure, but when pollsters fail to sufficiently take account of it, they tend to undersample one side and oversample the other. Take a CNN/ORC International poll released September 10 that found likely voters supporting the president over Romney by 52 percent to 46 percent. The sample was massively skewed toward Democrats, who made up 50.4 percent of those surveyed while Republicans and independents accounted for only 45.4 percent and 4.2 percent respectively.
Another factor could be the “bounce” Obama got from the Democratic convention, which fueled interest in voting among his base. The Washington Post/ABC poll found that “strong enthusiasm” among Obama supporters was up eight points after the convention.
That interest might be permanent or it could be very fleeting. We just don’t know.