Viewpoints: How Accurate Are the U.S. Election Polls?

According to the Gallup Accuracy Records in Presidential Elections, in 2012, the Gallup deviation between the final Gallup Survey and the actual election results, Obama performed 2% better and Romney 3% worse. In 2008, Obama performed 2% worse and McCain 2% better. And in 2004, Bush performed 1.7% better and Kerry .7% worse.

So are the 2016 polling predictions status quo, and which polls can you trust? - 6/2/16: The best-performing polls recently have been those from Monmouth University and those from Marist College. Both apply “gold standard” methodologies, using live telephone interviews and placing calls to cellphones as well as landlines…The answer may also depend on which polls you’re looking at. …polls that employ more expensive methodologies, and abide by higher levels of disclosure and transparency, tend to be more accurate than those that don’t. It may be that the best polls are roughly as accurate as ever but that the worst polls are increasingly far off the mark. - 6/20/15: How much can we trust the polls as we head toward the 2016 elections? …The best survey organizations, like the Pew Research Center, complete about two of the more expensive cellphone interviews for every one on a landline. For many organizations, this is a budget buster that leads to compromises in sampling and interviewing. …Those paying close attention to the 2016 election should exercise caution as they read the polls. Because of the high cost, the difficulty in locating the small number of voters who will actually turn out in primaries and the increasing reliance on non-probability Internet polls, you are likely to see a lot of conflicting numbers. - 8/18/16: Currently, 41% of registered voters say they would vote for Hillary Clinton if the general election were held today, while 37% say they would vote for Donald Trump, 10% say they would vote for Gary Johnson and 4% say they would vote for Jill Stein. - 8/18/16: The latest Rasmussen Reports national telephone and online White House Watch survey of Likely U.S. Voters shows Clinton with 41% support to Trump’s 39%. Libertarian candidate Gary Johnson picks up nine percent (9%) of the vote, while Green Party nominee Jill Stein trails with three percent (3%). Three percent (3%) like some other candidate, and five percent (5%) are undecided. - 5/3/16: There's good news for those still looking to polls for insight: In our study, polls, particularly when taken in aggregate, remain a very accurate way to predict elections, and big discrepancies between polls and results are more the exception than the rule. …As for the final poll averages published by RealClearPolitics before voting, the aggregation site correctly predicted the winner 90 percent of the time across the 49 contests covered. 

Since the conventions in July, more than 20 polls have shown Hillary Clinton ahead of Donald Trump. Will that lead last?