Welcome to DU!
The truly grassroots left-of-center political community where regular people, not algorithms, drive the discussions and set the standards.
Join the community:
Create a free account
Support DU (and get rid of ads!):
Become a Star Member
Latest Breaking News
General Discussion
The DU Lounge
All Forums
Issue Forums
Culture Forums
Alliance Forums
Region Forums
Support Forums
Help & Search
Explained: Margin of error
I think most people on DU are familiar with the sources of error in a poll, but this article from MIT News has a pretty good explanation. An excerpt:
In mid-October, a Gallup poll of likely voters nationwide showed former Massachusetts Gov. Mitt Romney leading President Barack Obama by a 7 percent margin. That same week, a poll by the University of Connecticut and the Hartford Courant, covering virtually the same time period, showed Obama ahead of Romney by 3 points. That's a 10-percentage-point disparity.
The Gallup poll reported a margin of error of plus or minus 2 percent, while the UConn/Hartford Courant poll reported a 3 percent margin of error—so even if you add the maximum claimed errors, that still leaves a 5-point disparity between the results. As some candidates have observed on the campaign trail, the math just doesn't seem to add up.
...
What does that margin of error figure actually mean? The definition is that 95 percent of the time, the sampled result should fall within that margin of the result you'd get by sampling everybody. But that also means that one time out of 20, the results would fall outside of that range—even if sampling error were the only source of discrepancies.
...
Another potential source of error, and one that's hard to quantify, is the nonresponse error. Pollsters begin by attempting to reach a certain randomly selected set of people that is representative of the overall population—for example, by generating a list of random phone numbers. But there are two problems: Sometimes nobody answers the phone, and even when someone does answer, they often—and increasingly—refuse to respond.
more ...
The Gallup poll reported a margin of error of plus or minus 2 percent, while the UConn/Hartford Courant poll reported a 3 percent margin of error—so even if you add the maximum claimed errors, that still leaves a 5-point disparity between the results. As some candidates have observed on the campaign trail, the math just doesn't seem to add up.
...
What does that margin of error figure actually mean? The definition is that 95 percent of the time, the sampled result should fall within that margin of the result you'd get by sampling everybody. But that also means that one time out of 20, the results would fall outside of that range—even if sampling error were the only source of discrepancies.
...
Another potential source of error, and one that's hard to quantify, is the nonresponse error. Pollsters begin by attempting to reach a certain randomly selected set of people that is representative of the overall population—for example, by generating a list of random phone numbers. But there are two problems: Sometimes nobody answers the phone, and even when someone does answer, they often—and increasingly—refuse to respond.
more ...
1 replies
= new reply since forum marked as read
= new reply since forum marked as read
