CHARLOTTESVILLE -- Negative political ads may be a good thing, at least according to research done by University of Virginia politics professor Paul Freedman and three colleagues.

Freedman and his co-authors found that negative ads, in particular those that draw contrasts between a candidate and an opponent's position on issues or past record, turn out to have the most measurable positive effects. The sorts of ads most disliked by pundits are the ones most likely to educate, engage and mobilize voters, they reported.

Candidates realize the importance of responding to opponents' ads that raise questions about their records, character or issue stances, so negative ads help hold candidates accountable, Freedman said.

The new research examined the political advertising of the 2004 election season and suggested that the ever-growing barrage of political ads -- both negative and positive -- actually helped to educate and engage citizens and only rarely had negative impact.

The research from Freedman and his colleagues is detailed in a new book, "Campaign Advertising and American Democracy," (published last month by Temple University Press).