February 11, 2009 2:07 PM
- Text
The Way Presidential Polls Work - Or Don't
The only thing predictable about presidential polls lately is how unpredictable they are. As the election draws near, new polls come out almost daily. But they often have very different results from the one that came before. How does this happen? CBS News senior political correspondent Jeff Greenfield runs the numbers.
You've heard this all before: Great news for Barack Obama! He's 13 points up. No, wait, great news for John McCain, he's only one point behind, or is it 3 ... or 7 ... or 10?
Well it's all of those. The spread between the candidates depends on which poll you're looking at. And it's the same with key states.
Obama's up either 2 points in Virginia or he's up 10 points in Virginia. McCain is up 1 point in Ohio or 12 points down in the Buckeye State.
How can that race vary this widely? Because of the way polls work - or don't work.
First, different polls make very different assumptions about who's likely to vote.
"If you assume that you have to have voted before, you probably undercount your voters," said CBS News polling director Kathy Frankovic. "If you trust them and when they tell you they're definitely going to vote, you may be representing them accurately. You may possibly be overestimating their share of the electorate."
Then, there's the cell-phone vote. Today, almost 12 percent of Americans don't have land line phones at all. Some polls - like ones conducted by CBS News - can reach them. But polls that use automatic dialing techniques can't.
"The cell phone-only people are disproportionately young, but not all of them are young. There still are a significant number of middle-aged folks who are only reachable on their cell phones," Frankovic said.
In fact one study shows polls that include "cell phone-only" folks give Obama 3 points more than polls that don't include such voters.
Another point: When a poll says it has a margin of error, you have to understand what it means. It means it could be off by 3 points in either direction for either candidate.
So, if Obama has a 50 to 45 lead, it could mean anything from a 53 - 42 edge, to a 48 - 47 edge for McCain.
Finally, some polls can be just plain wrong. And people can change their minds.
This is why Kevin Nealon on SNL years ago reported that "in a recent poll, 85 percent said if the election were held today - they'd really be surprised."
Copyright 2009 CBS. All rights reserved. You've heard this all before: Great news for Barack Obama! He's 13 points up. No, wait, great news for John McCain, he's only one point behind, or is it 3 ... or 7 ... or 10?
Well it's all of those. The spread between the candidates depends on which poll you're looking at. And it's the same with key states.
Obama's up either 2 points in Virginia or he's up 10 points in Virginia. McCain is up 1 point in Ohio or 12 points down in the Buckeye State.
How can that race vary this widely? Because of the way polls work - or don't work.
First, different polls make very different assumptions about who's likely to vote.
"If you assume that you have to have voted before, you probably undercount your voters," said CBS News polling director Kathy Frankovic. "If you trust them and when they tell you they're definitely going to vote, you may be representing them accurately. You may possibly be overestimating their share of the electorate."
Then, there's the cell-phone vote. Today, almost 12 percent of Americans don't have land line phones at all. Some polls - like ones conducted by CBS News - can reach them. But polls that use automatic dialing techniques can't.
"The cell phone-only people are disproportionately young, but not all of them are young. There still are a significant number of middle-aged folks who are only reachable on their cell phones," Frankovic said.
In fact one study shows polls that include "cell phone-only" folks give Obama 3 points more than polls that don't include such voters.
Another point: When a poll says it has a margin of error, you have to understand what it means. It means it could be off by 3 points in either direction for either candidate.
So, if Obama has a 50 to 45 lead, it could mean anything from a 53 - 42 edge, to a 48 - 47 edge for McCain.
Finally, some polls can be just plain wrong. And people can change their minds.
This is why Kevin Nealon on SNL years ago reported that "in a recent poll, 85 percent said if the election were held today - they'd really be surprised."
55 Comments +
Popular Now in CBS Evening News
- Toxic Japanese debris piles up on Alaska's shore
- 5/29: World responds to Syria massacre, Romney to clinch GOP nomination
- Vatican scandal could further grow
- Despite massacre, U.S. won't arm Syria's rebels
- "Super-agers": What it takes to live beyond 100
- Computer virus found in Iran
- Obama awards Medal of Freedom to Bob Dylan, John Glenn
- 5/28: Special tribute for Vietnam Veterans, Marines plea for extra benefits
- Concealed-weapons permits catch on in Colo. county
- Honoring fallen heroes with thousands of flags
- Wells Fargo helps housing recovery in Phoenix
- Marines seek benefits over contaminated water
- UN negotiator: Syria has reached the tipping point
- Calif. HS student devises possible cancer cure
- Plan in place for salvaging Costa Concordia
- CBS News marks six years since deaths in Baghdad
