Boston — To the undecided voters in our audience: Would you have an easier time choosing between John McCain and Barack Obama if their campaigns spent more time debating the same topics? Or would you learn more about them if each campaign emphasized the issues where it feels it has the upper hand? (Imagine – and this might not be too hard — that 90 percent of McCain’s issue ads were about counterterrorism and Iran, and 90 percent of Obama’s were about health care and economic stagnation.)

For many political scientists, the correct answer is obviously the first one: When campaigns debate the same topics – a phenomenon scholars call “issue convergence” — voters learn more about what each candidate believes, and democracy is better served.

But that assumption is not necessarily correct, according to a study presented this morning here at the annual meeting of the American Political Science Association. On the contrary, issue convergence does not seem to improve voters’ overall knowledge about a pair of candidates. And among the least engaged, least knowledgeable voters, issue convergence actually seems to impair knowledge about candidates and their policies.

Keena Lipsitz, an assistant professor of political science at Queens College of the City University of New York, looked at data from the presidential campaign season of 2000, beginning with detailed records of which commercials were aired by the George W. Bush and Al Gore campaigns in specific cities during specific weeks.

She found that when both Bush and Gore both broadcast ads on the same topic in the same city during the same week, that did not affect the accuracy of answers given by local residents contacted by the National Annenberg Election Study during those weeks. Issue convergence did not improve people’s ability, for example, to correctly tell the Annenberg surveyers which candidate supported school vouchers (Bush) or giving patients the right to sue their HMOs (Gore).

And among the subgroup of people who told the Annenberg survey that they follow politics “hardly at all,” issue convergence significantly reduced their performance on those questions. They did better in times and places where only one campaign was airing advertisements on the topic in question.

All of this suggests, Ms. Lipsitz said, that issue convergence is not as important as certain political scientists have made it out to be. “Candidate dialogue does not seem to help anyone learn during a campaign,” she writes in her paper. (The paper is available at the conference Web site.)

Ms. Lipsitz conceded that much more work needs to be done to confirm and clarify her finding, but her paper was praised during the panel by Scott L. Althaus, an associate professor of political science at the University of Illinois at Urbana-Champaign. “There are not many papers that go right to the core of some of the assumptions of democratic theory the way this one does,” he said.