MSNBC's Lawrence O'Donnell cackled with glee over an NBC/Wall Street Journal poll July 24 which showed President Barack Obama leading Mitt Romney, 49 percent to 43 percent. If he knew how to read polls, he'd have cried.
The purpose of a poll, ostensibly, is to find out what people think. But some polls are conducted to influence how we think.
On issues, responses vary dramatically, depending on how questions are worded. Eighty percent of respondents answered yes to this question: "Should laws be passed to eliminate all possibilities of special interests giving huge sums of money to candidates?" But only 40 percent said yes to this one: "Should laws be passed to prohibit interest groups from contributing to campaigns, or do groups have the right to contribute to the candidate they support?"
You can't slant a poll on candidate preference by how you word the question. But you can manipulate the sample.
Democrats have had, on average, a 3 percentage point advantage in turnout in presidential elections from 1984 on, according to exit poll data.
No one thinks President Barack Obama or his party will be as popular this time. The exit polls for the 2010 midterms showed Republicans and Democrats tied at 35 percent. In Gallup's annual survey in January, Democrats had a 4 point edge, 31-27. But that's the lowest percentage for Democrats since 1988.
It's one thing to answer a pollster's question, another to show up to vote. A Rasmussen survey of likely voters in June found Republicans leading, 35-34. In a Gallup poll in July, 51 percent of Republicans -- but only 39 percent of Democrats -- said they were "more excited about voting than usual."
The partisan breakdown in November figures to fall somewhere between the historic 3 point advantage for Democrats, and a tie. In the NBC/WSJ poll, Democrats outnumbered Republicans by 11 percentage points.
The RealClear Politics average of polls -- which on Monday showed President Obama leading, 46.4 percent to 45 percent -- more accurately reflects the state of the race. But even it overstates supports for Democrats.
Psephologist Jay Cost examined polls of registered voters by news organizations. On average, 5.5 percent more Democrats were polled. Collectively, the polls overstate support for President Obama by 2-3 percentage points.
Even exit polls -- which should be the most accurate, since they're taken right after people vote -- have overstated support for Democrats by about 2 percentage points. In 2004, exit polls predicted a win for Democrat John Kerry. In the recall election in Wisconsin in June, exit polls predicted a cliffhanger. Republican Gov. Scott Walker won comfortably.
So before you get excited, or depressed, by a poll, check its margin of error, and the partisan breakdown.
Most statistically valid polls have an MOE around 3. That means each number in it could be 3 points higher, or 3 points lower. So if a poll shows Candidate A leading Candidate B, 46-44, Candidate B actually could be ahead, 47-43.
Even garbage polls like the NBC/WSJ poll provide clues to the real score, if you know what to look for. Despite the enormous oversampling of Democrats, President Obama was below 50 percent, had only a 6 point lead. He trailed Mr. Romney by 2 percentage points among "high interest" voters.
Here are some other important facts about polls you usually aren't told:
• When a president runs for re-election, his percentage of the popular vote closely tracks his job approval. No president with a job approval below 50 percent has ever been re-elected.
• A challenger who is in a statistical tie with an incumbent president in midsummer is unusually strong, because the stature gap between the challenger and the president usually doesn't narrow until after the out party's nominating convention. This is especially so for GOP challengers, because they don't have journalists spinning for them. Often the first time voters hear the Republican side of an issue is when their advertising kicks in after Labor Day.
President Obama is in deep, deep kimche. I suspect Mr. O'Donnell knows this. He just doesn't want you to.jackkelly
Jack Kelly is a columnist for The Press and The Blade of Toledo, Ohio. firstname.lastname@example.org, 412 263-1476.