From the National Council On Public Polls:
Certainly, if the gap between the two candidates is less than the sampling error margin, you should not say that one candidate is ahead of the other. You can say the race is "close," the race is "roughly even," or there is "little difference between the candidates." But it should not be called a "dead heat" unless the candidates are tied with the same percentages. And it certainly is not a “statistical tie” unless both candidates have the same exact percentages.From CNN:
And just as certainly, when the gap between the two candidates is equal to or more than twice the error margin – 6 percentage points in our example – and if there are only two candidates and no undecided voters, you can say with confidence that the poll says Candidate A is clearly leading Candidate B.
When the gap between the two candidates is more than the error margin but less than twice the error margin, you should say that Candidate A "is ahead," "has an advantage" or "holds an edge." The story should mention that there is a small possibility that Candidate B is ahead of Candidate A.
(CNN) — With the dust having finally settled after the prolonged Democratic presidential primary, a new CNN/Opinion Research Corporation poll shows Sens. John McCain and Barack Obama locked in a statistical dead heat in the race for the White House.p.s. Yes, I was being being slightly facetious with the headline.
With just over four months remaining until voters weigh in at the polls, the new survey out Tuesday indicates Obama holds a narrow 5-point advantage among registered voters nationwide over the Arizona senator, 50 percent to 45 percent. That represents little change from a similar poll one month ago, when the presumptive Democratic presidential nominee held a 46-43 percent edge over McCain.
CNN Polling Director Keating Holland notes Tuesday's survey confirms what a string of national polls released this month have shown: Obama holds a slight advantage over McCain, though not a big enough one to constitute a statistical lead.
"Every standard telephone poll taken in June has shown Obama ahead of McCain, with nearly all of them showing Obama's margin somewhere between three and six points," Holland said. "In most of them, that margin is not enough to give him a lead in a statistical sense, but it appears that June has been a good month for Obama."[...]
The poll, conducted June 26-29, surveyed 906 registered voters and carries a margin of error of plus or minus 3.5 percentage points.