For All You Poll Watchers

via Political Wire:

Statistical Tie?

An interesting debate broke out in the comments on our post reporting the latest Pew Research poll that showed the presidential race narrowing. While the pollster claimed the race was now even because Obama's 46% to 43% lead over McCain was within the survey's margin of error, this is very misleading.

The survey clearly shows the race narrowing, but suggesting it's a "statistical tie" or "deadlocked" is not accurate. As Kevin Drum noted, what we're really interested in is "the probability that the difference between the two candidates is greater than zero -- in other words, that one candidate is genuinely ahead of the other."

So instead of reporting that any result within the margin of error is a tie -- something we're often guilty of -- it's more informative to show how probable it is that a candidate is actually leading. A simple spreadsheet shows that in the case of the Pew Research poll, there is a 94% probability that Obama is actually leading McCain.