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I know who will win the election (with some amount of certainty)
Well, it is almost election day, and many people are watching the polls. As a newcomer to teaching stats, I have enjoyed examining the polls while my students have enjoyed quizzes about margin of error and confidence intervals 
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The margin of error is the way that statisticians provide detailed information about the uncertainty associated with a particular estimate from a sample to a population. A key point that is misinterpreted all over the place is the fact that the margin of error reported in the media is generally the amount that should be added or subtracted from BOTH candidates estimated percentages in order to report the uncertainty!
A nice explanation is in this pamphlet on polling from the American Statistical Society: http://www.amstat.org/sections/srms/pamphlet.pdf
“A misleading feature of most current media stories on political polls is that they report the margin of error associated with the proportion favoring one candidate, not the margin of error of the lead of one candidate over another. To illustrate the problem, suppose one poll finds that Mr. Jones has 45 percent support, Ms. Smith has 41 percent support, 14 percent are undecided, and there is a 3 percent margin of error for each category.
If we note that Mr. Jones might have anywhere from 42 percent to 48 percent support in the voting population and Ms. Smith might have anywhere from 38 percent to 44 percent support, then it would not be terribly surprising for another poll to report anything from a 10-point lead for Mr. Jones (such as 48 percent to 38 percent) to a 2-point lead for Ms. Smith (such as 44 percent to 42 percent).”
Tags: explanation, margin of error, polls, statistics
