Mark Blumenthal | November 6, 2008
The Wall Street Journal's Numbers Guy Carl Bialik has a must-read post-election review on how the polls did and on the future of polling. Here is his bottom line:
[A]s Americans watched the news networks call states one by one for Mr. Obama and his Republican opponent, Sen. John McCain, Tuesday night, pollsters could breathe a sigh of relief. There wasn't a single big miss in the presidential race. Most polls showed virtual ties in Indiana, Missouri and North Carolina, and none of those states was decided by more than a point. "Pollsters generally did very well," says Mark Blumenthal, a former Democratic pollster and co-founder of Pollster.com.
Zogby International polled in eight states in the last week, including six of the closest races, and missed the final margin by an average of less than two points -- as accurate as the poll aggregators such as Pollster.com.
The lopsided nature of the race helped pollsters. Just seven states were decided by fewer than five percentage points, and just 15 by fewer than 10. That contrasts with 10 and 21, respectively, in 2004, and 12 and 22 in 2000. With that many close races in the past, it was more than likely you'd have at least one polling gaffe simply because of the error introduced by random sampling. Pollsters generally underestimated Mr. Obama's support in Nevada this year, and overestimated it in Iowa. But those misfires won't be judged harshly because he won both states by comfortable margins.
Bialik also considered the performance of polling aggregation sites like ours:
The biggest winners may have been poll aggregators, who were combining disparate polls as far back as 2002, but gained new members and reached a new level of national prominence this time around. Their advantage is twofold: Their composite results may dilute the effect of any error in one poll, and their results are more expansive, including regions that no one pollster can typically afford to cover. A dozen or so Web sites combined polls to forecast the election, and just about all of them put Mr. Obama's electoral-vote total at between 338 and 393; he likely will finish with 364 or 375. (Those that also forecast congressional races generally foresaw Democratic gains.)
At least two sites -- Pollster.com and fivethirtyeight.com -- also estimated the winning margin for each state, using poll data and their own formulas. They typically missed the margin by just 2.4 and 2.3 percentage points, respectively. Each site beat each of the 10 pollsters active in at least eight states, head to head, except for Zogby.
Bialik's companion blog item also has some useful links to ongoing discussions of voter turnout:
Perhaps the most interesting variable in the contest was among the hardest to predict: Voter turnout. While the popular-vote total so far has barely cleared the 2004 turnout of 122 million, several forecasters estimate that, once all ballots are counted, turnout will be between 125 million and 136.6 million. [Franklin & Marshall College statistician Brian] Adams and Sam Wang, a Princeton University neuroscientist and poll watcher, forecast turnout of 133 million and 135 million, respectively. Allan Keiter, of the forecasting site 270 to Win, may also have come close.
And he saves me the trouble of an "outliers" post for these "preliminary analyses of pollsters’ performance... Pollster.com, Huffington Post, the Atlantic’s Marc Ambinder and a Fordham University political scientist."