Culling never-before-used data about viewing habits, and combining it with more personal information about the voters the campaign was trying to reach and persuade than was ever before available, the system allowed Mr. Obama’s team to direct advertising with a previously unheard-of level of efficiency, strategists from both sides agree…

In essence, said Larry Grisolano, who helped lead the development of the system, it created a new set of ratings based on the political leanings of categories of people the Obama campaign was interested in reaching, allowing the campaign to buy its advertising on political terms as opposed to traditional television industry terms.

“We were able to create a set of ratings based on a model of our target voters, as opposed to the broader categories that are kind of defined by traditional advertising ratings,” he said.

Erik Smith, another senior strategist, said a decision by “super PACS” supporting Mr. Romney to hold off on their first major anti-Obama advertising push until well after the primaries had given the team extra time to develop its system.