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The Most Important Ads of the Campaign Are Only Airing Now

- November 1, 2012

HuffPo’s Jason Linkins asks:

bq. Dunno if @monkeycageblog takes requests, but I’d love to see some poli sci on when, on the campaign timeline, tv ads are most effective.

Here’s what we know, though admittedly we need to learn a lot more.  I’m cribbing from my old “Moneyball” post on 538.

The short story is that the effects of campaign ads decay.  Quickly.  This isn’t necessarily surprising, if you think of campaign messages as being delivered in “doses” that, like most medicines, wear off.  And this makes sense if you think that undecided voters are engaging, at least in part, in what is called “online processing“: updating their assessments of the candidates on the fly in response to new information, but not necessarily remembering the specifics of that information and thus making it possible for the next “dose” to affect them as well.

So how fast is the decay?  In the famous randomized experiment during Rick Perry’s 2006 gubernatorial campaign, Gerber, Gimpel, Green, and Shaw found that:

bq. …the current week’s advertising raises Perry’s vote share by 4.73 percentage points per 1,000 GRPs…a week later, the effects of these ads…receded to −0.17 percentage points.

The same was true in a study of the 2000 presidential campaign by Seth Hill, James Lo, Lynn Vavreck, and John Zaller.  From an earlier ungated version of their paper:

bq. Even when the persuasive effect of ads on candidate preference is large, 50 to 75 percent of the effect dissipates within the first week and almost all is gone by the end of the second week.

The rapid decay of advertising effects makes it hard to understand why, as Ryan Lizza describes, the Obama team was confident that their early advertising in the summer of 2012 would be so effective.  And it makes the Romney campaign’s strategy of waiting and spending a lot of money now seem sensible.

But the ultimate effect of these late ads depends on whether one side will have a definitive advantage.  As I noted in my earlier post, advertising effects emerge most clearly when one side can out-spend the other — and by a lot.  There are reports that Romney and his allied super-PACs will outspend Obama by 2-1 in the final week of the campaign.  But up until now, the cash advantage hasn’t translated into an ad advantage: Romney and the super-PACs have been paying higher rates and not necessarily putting their ads in front of more viewers.

So although this last week of advertising appears to be important, and probably the most important, we don’t yet know whether either the Democrats or Republicans will have enough of advantage to shift the polls — and shift them enough to matter — in the battleground states.