Has there been a convention bounce for Obama? If so, how large? Right now, only three polls are available to provide a measurement. This morning's Rasmussen poll (August 29-31) shows Obama ahead 49%-46%, which compares to a 46%-46% tie in the polling immediately before the convention (August 23-25). CNN has a new poll out showing Obama ahead 49%--48%, compared to 47%--47% just before the convention. Gallup shows a larger improvement, as a two-point McCain lead in the immediate pre-convention polling has now turned into a six-point Obama advantage.
On average, this shows a four-point improvement for Obama, although most polls have not released their post-convention numbers yet, thus leaving the size of the bounce unknown. However, beyond the net increase, the most important shift that occurred over the past week is the drop in the number of undecideds. Pollster.com illustrates this shift nicely (more in the extended entry):
This is the highest point for both candidates in the national trend. The ten day trend, starting at 9/1 with 8/22 trend in parenthesis, is particularly illuminating:
Obama: 48.4% (44.3%, +4.1%)
McCain: 45.7% (42.8%, +2.9%)
Currently, only 6.9% of the electorate is listed as either undecided or voting third party, compared to 13.9% ten days ago. The last ten days, starting with the Biden announcement, has moved more than half of all undecided voters off the fence.
This is why Obama's bounce is larger than it appears at first glance. He actually has gained significant raw support, as he has equaled, surpassed, or come within 1% of his all-time high in every recent poll. At the same time, McCain has gained raw support, thus making Obama's overall net gains minimal. However, a 1.2% net gain is actually pretty significant when it is coupled with such a large drop in undecideds. A 2.7% lead with 6.9% undecided or voting third-party is actually much, much larger than a 1.5% lead with 13.9% undecided. In the latter, McCain must defeat Obama by only 10% among the undecideds in order to force a tie, while in the latter he needs a whopping 40% victory among the undecideds to vote a tie.
Relative to the number of undecideds needed to win the election, Obama's advantage has actually quadrupled. Further, he now sits only 1.6%, or less than 25% of the current undecideds, from reaching the 50% threshold. Still, further, Republicans will not make any convention gains tonight, as they have cancelled the prime-time speeches for tonight's convention. Although, given that Bush and Cheney were speaking, I was kind of looking forward to tonight as the easiest way to tie McCain to Bush that we could find.