The "America Deserves Better" ad -- which assails Obama for a super PAC commercial that suggested Romney's Bain Capital business dealings contributed to a woman's death from cancer because she lost her health insurance -- moved "pure independent" voters not aligned with either party 6 percentage points toward Romney, the Vanderbilt University/YouGov Ad Rating Project study indicated.
"What is new here is that the 'America Deserves Better' ad seems to score points for Romney," Ad Rating Project leader and Vanderbilt political science Professor John Geer said.
"It was the first time among all the ads we have studied where a Romney attack moves down the president's numbers among pure independents," he said.
Obama distanced himself from that ad Monday, saying, "I don't think that Gov. Romney is somehow responsible for the death of the woman that was portrayed in that ad."
He pointed out the ad was produced not by his campaign but by an independent expenditure PAC called Priorities USA Action that supports his re-election.
"Keep in mind this is an ad that I didn't approve, I did not produce, and as far as I can tell, has barely run. I think it ran once," Obama told reporters.
Obama said that ad was far different from a Romney campaign ad, titled "Right Choice," that accuses the president of gutting welfare's work requirement, "which every single person here who's looked at it says is patently false."
He said his administration has said only that it would consider allowing states some flexibility in how to meet requirements but only if it helps welfare recipients find work.
Many fact checkers have corroborated Obama's position on the Romney campaign's welfare ad.
And while the ad is false, the Vanderbilt study indicated it was also ineffective in changing independent voters' minds -- although Democrats, Republicans and independents all said it was more memorable than "America Deserves Better," the Ad Rating Project study said.
The Romney campaign did not immediately comment on the Ad Rating Project research.
An Obama campaign ad that had a measurable effect in moving voters away from Romney was a spot featuring Romney singing "America the Beautiful" as the screen showed newspaper headlines and video clips of jobs sent overseas by companies controlled by Bain, which Romney co-founded.
For the research, Geer and his Ad Rating Project team showed the ads to a representative sample of 600 U.S. voters, with an oversample of 200 independent voters, to gauge their reactions.
The goal of the continuing research is to add greater statistical certainty to advertising effectiveness, Geer said.
YouGov, formerly Polimetrix, is a Web-based market research firm.