The concept of margin of error has been much discussed here in the last few days since clearly the morons who babble on TV don't get it. Now I know must people don't want to delve into the dark arts of the Integral Calculus, but TPM has a nice little explanation that makes it very clear what this is all about.
Margin of Error
In public opinion surveying, the margin of error refers to the expected range of variation in a poll, if it were to be conducted multiple times under the same procedures. This is not necessarily indicative of a true result, but establishes a statistical average within which most polls will line up. As an example, if a Democratic candidate has 47% in a poll and the Republican 45%, with a ±4% margin of error, the poll could potentially show the Democrat as high as 51% or as low as 43%, and the Republican ranging from 41%-49%, if the poll were repeated. In statistical terms, the margin of error is typically established for a 95% confidence interval, meaning that the officially listed variation will occur in 19 out of 20 times that a poll is conducted -- but also that in 1 of 20 cases, a pollster will produce a result that lies far outside the norm.
http://talkingpointsmemo.com/...