Going into September, Hillary Clinton has a sizable advantage over Donald Trump: five percentage points in the RealClearPolitics’ polling average. The Upshot, the New York Times’ polling blog, gives Clinton a 90 percent chance of winning the presidency, while British Sky Bet gives Clinton four times as good a chance as Trump.
As South Carolina voters head to the polls Saturday to cast ballots in the GOP presidential primary, new survey data suggests the race has shifted in the final week, with GOP frontrunner Donald Trump losing some support in the state.
When Donald Trump announced he was running for president on June 16, the idea seemed faintly ridiculous. The Washington Post said that he faced “an uphill battle to be taken seriously by his rivals, political watchers and the media.”
David Brady is a Davies Family Senior Fellow at the Hoover Institution; the Bowen H. and Janice Arthur McCoy Professor of Political Science and Leadership Values in the Stanford Graduate School of Business; and a professor of political science at Stanford. Douglas Rivers is a senior fellow at the Hoover Institution and a professor of political science at Stanford University. An expert on survey research, he is also chief scientist for YouGov PLC, an international, Internet-based polling firm. Brady and Rivers discuss polling and how to measure change over time.
There are many sources of uncertainty in election polling other than sampling error. One source of error that looms large in this year's closest races is undecided voters -- people who say they are going to vote, but don't know (or won't say) which candidate they prefer.