Do The Ryan Bounce!
Nate Silver reads the post-Ryan polls with what he calls a “Vice Presidential Bounce adjustment”: namely, the increase in the polls every candidate gets thanks to the excitement of and exposure from a VP announcement, a bounce that fades over the next few polls. Silver calculates this as +4 points; in his words, “subtract four points from any poll conducted in between the naming of the running mate and the party convention” to get the candidate’s true polling position.
Applying this to Romney’s post-Ryan polls gives
a rather pessimistic forecast for Mr. Romney — giving him just a 24 percent chance of winning the Electoral College, rather than 31.3 percent as in the official version.
The intuition behind this is simply that, under this theory, it’s a bad sign for Mr. Romney that Mr. Ryan has produced a below-average bounce so far. Among the polls that allow for a direct comparison, Mr. Romney has gained an average of about one percentage point since his selection of Mr. Ryan.
[…] From what we can tell, most other candidates have gotten larger bounces after naming their running mates.
Of course, the story of polling is in the states, specifically the swing states, which tell a slightly different story. As Silver notes, even a one-point change in a swing state can look meaningful, and Romney did get a bounce in those states—though once adjusting for the VP announcement, the bump rarely exceeds one point.
Long blah short: it looks like Ryan is giving Romney a slight boost in swing states, which was his role. But if this is the best he can do—i.e., if Ryan’s actual campaigning is unable to sustain the excitement of his arrival, or if he (very probably) gets bogged down in a Medicare back-and-forth—the total benefit to Romney will be slim.
Of course, it’s entirely possible that the appearance of a bounce can be spun into “momentum”—the exact phrase the Romney campaign is using this morning—to convince voters that Ryan really is the game-changer they want him to be, in which case reality will follow its statistical derivation. But given that, as Greg Sargeant points out, we’re only five days past Ryan’s announcement and still talking about Romney’s taxes, the idea of any long-term momentum seems unlikely. More likely: this, and the post-convention bounce, will be the highest Romney polls until November.