In day-to-day radio ad spending by both candidates, per Clear Channel's analysis, Obama outspent McCain by a remarkable factor of 5-to-1 in radio advertising with the company--a 98% increase through September, compared to the midterms in 2006. Other leading radio groups also posted big gains in political advertising revenue compared to previous election years.

While Clear Channel did not share the precise revenue figures, in 2008 the radio business as a whole got about 10% of total broadcast budgets for political advertising, according to TNS--which should equal about $200 million. That's just a fraction of local broadcast's 70% share--equal to about $1.4 billion, but still a much-needed boon to the struggling radio business.

It might not come as a surprise that Obama outspent McCain in radio, as he outspent him in every other medium as well. Obama broke fund-raising records with his $150 million haul in September. However, Obama's 5-1 radio lead was bigger than his TV margin, where he led McCain by about 3-1 earlier this fall, but just 3-2 in the final weeks before the election.

Altogether, Obama spent about $250 million on advertising versus $130 million from McCain, for a 2-1 ratio. (Less, if you count some of the $80 million spent by the Republican National Committee on various races, including McCain's.)

Obama also made radio the centerpiece of his final media push in states like Pennsylvania, at least in terms of the total number of ad messages broadcast. McCurdy said Obama ran about 650 radio spots in the Philadelphia market in the week of Oct. 27 versus about 540 local TV spots and 120 cable TV spots. This data was produced by Candidata, a new service that Clear Channel developed to allow campaigns and political agencies to track their opponents' media activity.

In addition, McCurdy said Obama's campaign took a more nuanced approach to radio advertising, including identifying a handful of key demographic segments that would be targeted with different ad messages: adults 18-34, adults 35+ and women 35+. They reached these groups via networks created by Clear Channel targeting listeners in key battleground states, like Florida, Colorado, Ohio, Virginia, and North Carolina.

Overall, Obama spent about 70% of his ad dollars in states that voted for George Bush in the 2004 election, while McCain opted for a defensive strategy--trying to hold onto key red states, according to the Wisconsin Advertising Project hosted by the University of Madison-Wisconsin.

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