On average, a candidate who dominated advertising in a region raised his vote total by just 0.5 percent in the control group of voters in non-battleground counties, Ridout and fellow researcher Michael Franz found. They concluded that advertising "is responsible for only a small portion of the final result."
A University of Texas study of the 2000 and 2004 races found that Bush improved his standing by just 0.1 percent under virtually similar circumstances.
This is not to say that an advertising blitz can't sometimes play a definitive role in some races — or in certain stages of races. Advertising, for example, appears to play a far bigger role in primary and local elections where the candidates aren't as well known to voters and where a well-funded campaign can overwhelm poorer rivals. Gregg Phillips experienced the phenomenon firsthand.
Phillips managed Winning Our Future, the super PAC that backed former House Speaker Newt Gingrich in this year's Republican primaries. He points out that Romney and the independent group backing him all but buried his GOP opponents, particularly Gingrich, in the Florida primary in late January. Romney and his backers spent more than $11 million on TV ads, compared with less than $2 million by Gingrich. "Newt said, 'I threw the kitchen sink at him, but Romney threw a bigger sink at me,' " Phillips said.
Phillips and other strategists acknowledge that ads don't work the same way in a general election. By the summer and fall of an election year, the major candidates are usually well known, and TV advertising is just one way people form perceptions about them. There are many other sources of information: constant news coverage, campaign rallies, phone calls and home visits by campaign workers, as well as input from friends, family and co-workers.