If it seems the overwhelming majority of political ads on television this fall have been negative, you’re right. In fact, it seems to be getting worse.

A new report from the Annenberg Political Fact Check, a project of the Annenberg Public Policy Center of the University of Pennsylvania, finds that more than 80 percent of ads purchased by both political parties’ campaign committees have been attack ads.

But while Republicans and Democrats are both in negative mode, their method of attack differs. National Republican Campaign Committee (NRCC) ads tend to attack their opponent’s character while Democratic Congressional Campaign Committee (DCCC) spots usually focus on policy issues or the opponent’s political record, the study says.

Annenberg analyzed all ads by the DCC and NRCC that aired in the top 101 TV markets since Labor Day, copies of which were supplied by the Campaign Media Analysis Group.

It found that of 115 NRCC ads, 91 percent were negative while 81 percent of DCCC ads were negative.

“We found very few on either side that were all positive, but the DCCC's contained more mixed or ‘comparative’ ads  – a mix of positive statements about the supported candidate and negative statements about the opponent,” says the report, available at Factcheck.org.

Of the negative ads, 25 percent of the NRCC ads were character attacks or indictments of the candidate’s professional lives outside of politics, compared with 14 percent for DCCC ads.

Interestingly, the NRCC did have a greater percent of purely positive ads, 6 percent, than the DCCC at 2 percent.

Annenberg did not do the same study in years past, so it’s difficult to say whether the number of negative ads has risen, but many say anecdotal evidence points to yes.

This is for several reasons. For one, an increasing number of political ads are third-party spots not placed by the candidates themselves, and their creators seem to take even greater liberties with the truth.

But it’s also true that negative campaign ads work.

A recent study by Notre Dame found that negative 14 percent of viewers who saw a negative ad that attacked their favored candidated weakened their support for that candidate during the 2004 presidential campaign.

Other studies have found that negative ads, usually launched by underdogs, force the leading candidates to address obscure issues that push them off topic and impede them from discussing more relevant issues, thus sapping their momentum.

The Annenberg report specifically cites a number of ads, both Democrat and Republican, where the so-called facts are twisted or outright false occur. For example, one NRCC spot attacking New York Democratic House of Representatives candidate Michael Arcuri accuses the candidate, now serving as the Oneida County district attorney, of billing taxpayers for a call to a fantasy sex hotline.

Actually, an aide in Arcuri’s hotel room accidentally called the line while trying to get through to a business with a similar telephone number and hung up immediately, accruing a $1.25 charge.

The NRCC ad includes a woman’s voice purring suggestively and then asks: “Who calls a fantasy hotline and then bills taxpayers? Michael Arcuri.”

Democrats aren’t innocent, either. One recent ad accused Florida Republican Rep. Clay Shaw of profiting from a measure affecting drug benefits, though there was found to be virtually no supporting evidence.