In a new study, the project says the campaigns of Republican John McCain and Democrat Barack Obama have aired more than 100,000 ads since the end of the nomination season June 3, ABC News reported Wednesday.

The figure represents an increase of more than 20 percent over the 77,000 ads that ran in the summer of 2004 even though that presidential nomination period ended much earlier, the University of Wisconsin project said.

This summer voters in Pennsylvania, Ohio, Michigan and Wisconsin are seeing the most advertising.

In addition to counting the number of ads, the Wisconsin Advertising Project examined hem to see whether they attacked the opponent or dealt only with the candidates' strengths or message.

The project rated more than 90 percent of the Obama ads as positive in nature and approximately one-third of the McCain ads as negative.